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THE GIFT OF
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IRRIGATION
IRRIGATION:
ITS PRINCIPLES AND PRACTICE
AS A BRANCH OF ENGINEERING
BY
SIR HANBURY BROWN, K.C.M.G.
Membtr ijf the butitution of Ci'vil Engineers
(lati Royal EngineertJ
THIRD EDITION REVISED
LONDON
CONSTABLE & COMPANY LTD
to ORANGE STREET LEICESTER SQJJARE WC
1920
^. VAN NOSTRASB fiSMf AJJ?
Printed in Grtat Britain.
PREFACE TO THE THIRD EDITION.
The primary object of this book, as stated in the original
Preface which follows, is to set forth " guiding principles."
These do not change with lapse of time. But some of the works,
or matters connected with them, which, in previous editions,
have been made use of as illustrations of the application of
those principles, have advanced a stage in their growth or
development since they were so used. Still, that does not alter
their value as illustrations in their previously existing states.
Consequently, as this book deals with principles, and only with
works so far as they illustrate those principles, it has been
decided that nothing would be gained by making alterations
in the text because the works, projects or estimates, cited as
illustrations, are not now as they were at the time the previous
edition was published. But to avoid conveying any wrong
impression of actual facts by adopting this course, Appendix IV.
is added to this third edition with the object of drawing atten-
tion to any changes that have taken place, whenever it seems
desirable to do so.
PREFACE TO THE FIRST EDITION.
Irrigation is a subject which covers much ground, and
cannot be confined within the narrow boundaries of a single
volume. But the principles on which Irrigation Engineering
is based can be collected in small compass, and be illustrated
by examples of actual practice to the extent that space allows.
What, therefore, this work attempts to do is to set forth the
guiding principles that should govern the practice of irrigation,
and to furnish illustrations of their application in existing canal
systems. The majority of the illustrations have been selected
from the wealth of material that the irrigation experience ot
India and Egypt supplies, for the following reasons. In the
first place, I have been personally connected with irrigation in
both countries, and can therefore handle the facts, relating to
them, as one having authority on the subject, and " not as the
scribes," whose methods I might be imitating were I to draw
my illustrations from the records of other countries. In the
second place, it is India that furnishes examples of irrigation
on the largest scale, and that has been the school in which all
British irrigation engineers, previously to England's occupa-
tion of Egypt, have undergone their training. Moreover, the
excellent standard work on the subject, " The Irrigation Works
of India," by R. B. Buckley, C.S.I. , provides in a convenie t
form more than enough material for copious illustrations, and I
have made much use of it, with Mr. Buckley's kind permission.
But it will be found that Egypt has been the favourite source
of my borrowing. There are two good (so it appears to me)
reasons for this. The first is that I am intimately acquainted
with Egypt as an irrigating country. The second is that Egypt
is par excellence the country of irrigation, as it is wholly depen-
dent for its existence on its mother, the Nile, from which it has
never been weaned.
viii PREFACE.
Engineers entrusted with the execution of important works,
such as, for instance, high reservoir dams, would naturally not
be content with what they might find on the subject in a book
treating of irrigation generally, but would apply themselves to
a study of some work dealing exclusively with the special
subject of Dams. And so also with other matters which
require ample space for adequate description. Concerning
such this work attempts no exhaustive treatment, as being
beyond the compass of its embrace.
I am much indebted to Mr. R. B. Buckley, C.S.I., for valuable
suggestions and much assistance in obtaining and shaping the
subject-matter of this book. I am also under obligations to
Mr. W. B. Gordon, Director of Irrigation, Cape Colony, and to
Mr. W. L. Strange, Director of Irrigation, Transvaal, for
sending me information about their charges. The develop-
ment of irrigation schemes in South Africa is, however, not
sufficiently advanced for illustrations to be obtained from the
reports sent me. To Mrs. A. T. Kemble my grateful acknow.
ledgments are due for her kind assistance in the compilation
of the Index; and to Lady Brown, more than to any beside,
for relieving me of all the labour of preparing this work for
publication other than that of authorship only.
Among the works consulted in the preparation of this book,
the following are perhaps those from which I have borrowed
most : " The Irrigation Works of India," by Buckley ;
" Egyptian Irrigation," by Willcocks ; " Manual of Irriga-
tion Engineering," by Wilson ; " Irrigation du Midi da
I'Espagne," by Aymard ; Transactions, American Society of
Civil Engineers, International Engineering Congress, 1904,
" Irrigation " ; Report by Sir WiUiam Garstin, G.C.M.G.,
upon the Basin of the Upper Nile ; " Design and Construc-
tion of Masonry Dams," by Wegmann ; "The Improvement
of Rivers," by Thomas and Watt ; Proceedings of the
Institution of Civil Engineers,
TABLE OF CONTENTS.
CHAPTER 1.
IRRIGATION AND ITS EFFECTS. PAGE
Irrigation makes good Deficiencies of Rainfall in India- -America —
Egypt— Mesopotamia— Results in Egypt, India, United States of
America, France, Italy and Spain ...... i
CHAPTER II.
BASIN IRRIGATION.
Earliest Form — Natural Inundations — Evolution of a Basin System
— Programme of Filling and Emptying Basins— Dimensions of
Basin Banks — Inundation Canals of India — System in South
Africa 12
CHAPTER III.
PERENNIAL IRRIGATION AND WATER " DUTY."
Perennial System of Irrigation — Preparation of Project — " Duty" or
Water a8
CHAPTER IV.
SOURCES OF SUPPLY.
Sources Enumerated — Wells — Rivers — Lakes — Artificial Reservoirs
— Prevention of Loss by Evaporation and Absorption — Control
of Natural Lakes — Storage a Necessity in Egypt, India, America,
South Africa — Reservoir Sites — Diversion of Rainfall from one
Catchment to another — Indian Tank System • • • ■ 43
CHAPTER V.
DAMS AND RESERVOIRS.
Necessity of Storage Reservoirs — Rainfall and Flow-off— Waste Weir
Capacity — Reservoir Capacity — >Dams Classified and Discussed
— Earthen Dams — American " Loose-stone " and " Rock-fill "
Dams — Pressure in Masonry Dams — Submergible, Insubmergible
and Pierced Masonry Dams — Reinold's Gates . . . . 63
X TABLE OF CONTENTS.
CHAPTER VI.
MEANS OF DRAWING ON THE SUPPLY. PAGE
Lifting Machines —River Regulators — Anicuts — Barrages — French
Types — Site of Work — Different Types of River Regulators
Described and Discussed — Pumping Stations .... 104
CHAPTER VII.
METHODS OF CONSTRUCTION.
Materials Used — Method of Enclosing Area and Pumping — Well
Sinking — Cement Grouting — Iron Syphons Floated into Place
and Sunk 141
CHAPTER VIII.
MEANS OF DISTRIBUTION.
Channels of a Canal System Classified and Discussed — Silt —
Irrigation Canals — Drains J71
CHAPTER IX.
MASONRY WORKS ON IRRIGATION CANALS.
Works Classified — Head Sluices — Regulators — Escapes — Falls —
Fayfim " Nasbahs '' — Regulating Apparatus — Aqueducts, Super-
passages, Level Crossings and Syphons ..... igo
CHAPTER X.
METHODS OF DISTRIBUTION OF WATER, ASSESSMENT OF RATES, AND
ADMINISTRATION.
Distribution at the Head of the Canal System — Method of Assess-
ment — Rotation System as Applied in Different Countries —
Custom of " Priorities," United States of America— Water Rates
— Administration by Government, Association and Syndicate
Advantage of State Control .... ... 212
CHAPTER XI.
FLOOD BANKS AND RIVER TRAINING.
Effect of Flood Banks — Nile Banks— Breaches, how caused — Neces-
sary Precautions— Protective Works — Training Works . . 237
CHAPTER XII.
AGRICULTURAL OPERATIONS AND RECLAMATION WORKS.
Knowledge of Agricultural Needs Necessary— Over- watering— Re-
clamation of Salt Lands— Pumping Stations for Drainage and
Reclamation •<•..,..
250
TABLE OF CONTENTS. xi
CHAPTER XIII.
NAVIGATION. PAGE
Conflicting Opinion on Subject of Combining Irrigation and Naviga-
tion — Lock Sites — Lock Chambers, Gates and Sluices — Cracks
in Locks 358
APPENDIX I.
WEIGHTS AND MEASURES . . 867
APPENDIX 11.
FORMULAS AND DISCHARGE MEASUREMENTS . . jGg
APPENDIX III.
BOOKS OF KEFERENCB 278
APPENDIX IV.
NOTES 1919 , • • '°^
LIST OF PHOTOGRAPHIC
ILLUSTRATIONS.
>
Facing page
Platk I. AssuAN Dam gy
II. Water-lifting Wheel, Egypt .... 105
III. Water-lifting Wheel, Spain 106
IV. Dam on the River Genil, Spain .... log
V. RiVBR Spur, Spain ... ... no
VI. The Delta Barrage, Egypt 128
VII. Delta Barrage, West Weir under Construction 160
VIII. KosHESHAH Escape 195
IX. Mex Pumps under Erection . t , i 1 256
LIST OF FIGURES.
Fig.
CHAPTER II.
Diagram of a Natural Inundation . .
Diagram of Inundated Basins .
Sketch Map of Imperfect Basin System
Sketch Map of Improved Basin System
Diagram of Flood Canal. . . .
CHAPTER IV.
Map. The Nile above Khartoum
page
H
14
15
17
20
S3
CHAPTER V.
7. Croton Dam, Earthen Length ..... 76
8. FoY Sagar Tahk Dam 77
9. Kair Tank Dam 78
TO. Castlewood Reservoir Dam So
Ti. Betwa Dam 82
12. La Grange Dam 83
13. Vyrnwy Dam 84
14. Croton Dam, Submerqiblb Length .... 85
15. Henares Weir 85
16. NiRA Dam ,86
17. FuRENS Dam 87
18. Periyar Dam 88
ig. Marikanave Dam .... ... 89
20. Croton Dam, Insubmergible Length .... go
21. Zola Dam ... 93
22. Bear Valley Dam 93
23 and 24. Spanish Under-sluices 94
25. Bhatgarh Dam 95
26. AssuAN Dam . 97
37. Reinold's Gate . t » • loi
XIV
LIST OF FIGURES.
CHAPTER VI.
Fig. 38. Diagram of Perennial Canal .
ag. Narora Weir, Original
30. Narora Weir, Strengthened .
31. Narora Weir, Observation Pipes
33. Narora Weir, Pressure Diagram
33. Chenab Weir ....
34. Delta Barrage Weir
35 SoNE Weir Section .
36. SoNE Weir Crest Shutters .
37. Stoney's Gates ....
38. The Delta Barrage Channels
39. Delta Barrage Section .
40. Diagram of Water Levels, Delta Barragii
41. 2iFTA Barrage
PAGE
III
"5
"5
118
120
122
122
123
123
127
128
129
133
CHAPTER VII.
42. Method of Closing Springs by Vertical Pipes .
43. Method of Closing Springs by Horizontal Pipes
44. Cast-iron Piles
45. Grouting Apparatus for Piles
46. Well Intervals, Shubra .
47. Apparatus for Grouting Blocks .
48. Grouting Method for Foundations
49. Grouted End Wall of Lock .
50. Grouting Bores in Delta Barrage
51. End of Pipe Syphon .4 . . .
148
148
151
156
158
162
162
i6s
169 ;
CHAPTER VIII.
52. Sections of Main Canals.
53. Distributary Cross-section
179
182
CHAPTER IX.
54. Trebeni Canal Head-sluice
55. Kosheshah Escape
56. Fall with Cushion . .
57. Notch Fall.
58. Form of Notch .
39. Horizontal Closing Plank
191
194
196
196
198
301
LIST OF FIGURES. XV
CHAPTER IX.—continued.
PAGE
Fig 6o. Nadrai Aqueduct 205
61. NiRA Canal Super-passage 209
63. Ravi Syphon 210
63. Kao Nullah Syphon 211
64. Chenab Canal Syphon 211
CHAPTER XI.
65. Nile Banks 239
CHAPTER XIII.
66. ZiFTA Barrage Lock, Plan 265
67. ZiFTA. Barrage Lock, Section 265
68. AssuAN Dam Lock 266
INDEX 287
IRRIGATION:
ITS PRINCIPLES AND PRACTICE AS A
BRANCH OF ENGINEERING.
CHAPTER I.
IRRIGATION AND ITS EFFECTS.
Irrigation is the artificial process of supplying water to
crops in countries where the rainfall is either insufficient or
comes at the wrong season for their cultivation. Though
agricultural in its object, it has now become a special branch
of engineering on account of the nature of the works required
for the control of water.
The inequalities in the distribution of rainfall are not only
those that relate to time, but also to place. The rainfall of one
region may be abundant, of another the reverse. The rainfall
of certain seasons of the year may be heavy, while that of
other seasons may be light or wanting altogether. In some
countries the inequalities of both kinds are not sufficiently
pronounced for a distinction to be made between regions of
abundant and of scant rainfall, and between rainy and dry
seasons. In such countries, if the rainfall exceeds a certain
minimum, irrigation is not a necessity ; England and the north
of France are under such conditions.
In India the variations of rainfall, both as to place and time,
are extreme. In Sind and parts of the Punjab the average
I. B
2 IRRIGATION.
rainfall of the year is 3 inches only; in the Central Pro-
vinces the annual rainfall is, in places, from 50 to 60 inches ;
while in the mountains of the west coast and in the Himalayas
it varies from 50 to 100 inches and is sometimes as high as
150 inches. The distribution in time is as unequal as the distri-
bution in place. In the Madras Province 12 inches of rainfall,
or about one quarter of the total annual amount, is sometimes
recorded in twenty-four hours.
So also in the United States of America, the conditions of
the country range from arid to humid in consequence of wide
variations in the rainfall.
Egypt may be selected as an example of a country under
extreme conditions of another sort : it has neither rainy region
nor rainy season, and, as far as agriculture is concerned, may
be reckoned rainless. But hydrographically it should not be
taken alone. Its creation and continued existence is due
entirely to the fact that it is a portion of the Nile country,
which has its rainy regions in Abyssinia and the Sudan ; and
that it lies on the track of the run-off of the rainfall. It is this
that makes irrigation in Egypt possible. So it is with all irriga-
tion systems — the country irrigated must lie on the track of the
run-off of the rain that falls in the catchment area to which
it belongs. For rainfall is the primary source of all irrigation,
even of that effected from wells.
The scientific land boundary between nations, from an
irrigation point of view at any rate, is the water-shed, or line
separating catchment areas, whether it be mountain ridges or
desert wastes. In the case of the Nile country this principle
has been of late years upheld so far as was politically possible,
but the possession of the upper reaches of the Blue Nile by
Abyssinia stands in the way of any project for utilising Lake
Tsana as a storage reservoir for the benefit of the Sudan and
Egypt, to which hydrographically it belongs.
The water that is utilised for irrigation must naturally have
fallen as rain somewhere in the catchment area above the point
IRRIGATION AND ITS EFFECTS. 3
at which it is applied to the land surface. There are some
countries which, though their rainfall is so small as to be an
absolutely negligible factor in agriculture, have still been
renowned for their prosperity, for wealth of crops, and for
advanced civilisation in days long past. The best known
instances are those of Egypt and Mesopotamia, the lands of
the Nile and the Euphrates. Both these rivers in their natural
state annually flooded the lands bordering their lower reaches,
so that the rain that had fallen in the region where their sources
lie was spread over the surface of the country, and a natural
system of irrigation by inundation resulted. In Egypt this
natural inundation was assisted and controlled by artificial
banks and means of regulation with such success that in the
time of Joseph " all countries " came into Egypt to buy corn ;
and, later on, the land of the Nile became the granary of Rome.
The artificial system of irrigation which grew out of the
natural peculiarities of the Nile is known as the basin system ;
and is to be found, even to-day, on a vaster scale and in a more
elaborately developed stage in Egypt than anywhere els 2 in
the world. It was under this system that Egypt attained to
the heights of civilisation which it reached under the Pharaohs
of the old dynasties.
But the evolution of the Chaldean civilisation seems to have
advanced along other lines. For, though it is probable that
the newly arrived descendants of Noah found the plain in the
land of Shinar dependent for its agriculture on the annually
recurring floods of the Tigris and Euphrates, and that they,
their predecessors or successors may have introduced some
artificial control of the natural inundation, as the Egyptians
did, still it is improbable that the later prosperity of Babylonia
in the time of Nebuchadnezzar was the result of basin irrigation.
In Egypt the flood season is sufficiently early to allow time for
the maturing of a winter crop of corn or clover, sown after the
subsidence of the flood. In Mesopotamia the flood season is
six months later, so that when the waters retire, the parching
B 2
4 IRRIGATION.
summer has begun, when no rain falls to mitigate the scorching
heat. Under the extreme conditions of heat and dryness
which prevail in summer, it would be lost labour to sow seed
which, though it might germinate, would wither away before
coming to maturity. So that it would seem that the fertility
of the country and the opulence of its cities, as described in
Hammurabi's inscription (b.c. 2200), in the Bible, and also by
Herodotus, must be ascribed to the introduction and develop-
ment of a system of perennial irrigation such as we are now
pleased to call " modern." The material traces of the canals
still exist, and testify to the enterprise and skill of the hydraulic
engineers of Chaldea. Hammurabi, one of the greatest
monarchs of Babylonia's history, and perhaps a contemporary
of Abraham, thus describes in an inscription, older than the
Bible record, the effect of irrigation in ancient Chaldea : —
" I have made the canal of Hammurabi, a blessing for the
people of Shumir and Accad. I have distributed the waters
by branch canals over the desert plains. I have made water
flowin the dry channels, and have given an unfailing" (perennial)
" supply to the people. ... I have changed desert plains into
well-watered lands. I have given them fertility and plenty,
and made them the abode of happiness."
Such results we shall find attend irrigation wherever it is
introduced. Fertility and plenty is the sure return. And
neglect of the canal works as surely brings ruin. The basis of
Babylonia's prosperity and the cause of her decline appear to
be indicated in the following passages from the Bible (Jer. li.
13, 42 and 43) :—
" O thou that dwellest upon many waters, abundant in
treasures, thine end is come. . . ."
" The sea is come up upon Babylon : she is covered with
the multitude of the waves thereof; her cities are become a
desolation, a dry land, and a desert."
It is doing no violence to the text to assert that " the sea "
in this connection is the Euphrates in flood. In Cruden's
IRRIGATION AND ITS EFFECTS. 5
"Concordance" (i8i7)under "Sea" is to be found this explana-
tion : " The Arabians, and Orientals in general, sometimes
give the name of sea to great rivers, as the Nile, the Euphrates,
the Tigris, and others, which by their magnitude, and by the
extent of their overflowings, seem as little seas or great lakes.
Hence the country of Babylon, which was watered by the
Euphrates, is called 'thedesertofthesea' (Isa.xxi. i). Jeremiah
speaks of it in the same manner (Jer. li. 36) : ' I will dry
up her sea, and make her springs dry.' " The Egyptians to-day
call the Nile the Bahr el Azam, the most excellent - sea.
Shurippak, the city where Hasisatra, the Noah of the Chaldean
Deluge, received his orders to build a ship to save him in the
coming flood, was on the banks of the Euphrates. So that
the earliest record of any flood was of one in the Euphrates
valley.
The latter of the two verses quoted above is remarkable for
stating that a flood of waters had for result " dry land and a
desert." A passage in the Memoirs of Commander Felix Jones,
of the Indian navy, quoted in a lecture delivered by Sir
William Willcocks on March 25th, 1903, in Cairo, on the
" Re-creation of Chaldea," is in striking agreement with this
text, and goes far to explain it. The passage is this : —
" The summit of Opis,^ as we gaze around, affords a picture
of wreck that could scarcely be conceived, if it were not spread
at the feet of the beholder. Close to us are the dismembered
walls of the great city, and many other mounds of adjacent
edifices, spread like islands over the vast plain, which is as
bare of vegetation as a snow tract, and smooth and glasslike
as a calm sea. This appearance of the country denotes that
some sudden and overwhelming mass of water must have pros-
trated everything in its way, while the Tigris, as it ancientlj
flowed, is seen to have left its channel, and to have taken its
present coursfe through the most flourishing portion of the
• The ruins of Opis are on the Tigris above Baghdad, at the point where
the head works of the ancient canals would have been situate.
6 IRRIGATION.
district, severing in its mad career the neck of the great
Nahrwan artery, and spreading devastation over the whole
district around. Towns, villages and canals, men, animals and
cultivation, must thus have been engulfed in a moment, but
the immediate loss was doubtless small, compared with the
misery and gloom that followed. The whole region for a space
of 250 miles, averaging about twenty in breadth, was depen-
dent on the conduit for water, and contained a population so
dense, if we may judge from the ruins and great works
traversing it in its whole extent, that no spot in the globe
perhaps could excel it. Of those who were spared to witness
the sad effects of the disaster, thousands — perhaps millions —
had to fly to the banks of the Tigris for the immediate preser-
vation of life, as the region at once became a desert, where
before were animation and prosperity."
Thus Mesopotamia furnishes an example of a country which
flourished exceedingly by reason of its irrigation works, and
fell to utter ruin when these works were overwhelmed. Some
day, in the fulness of time, the successors of the Chaldean
engineers will lay firm hands upon the twin rivers and compel
them to the service of the lands through which they flow, that
the good that has been may be again when the time of
regeneration shall come. Already a beginning has been made.
Egypt also, when the British Occupation oegan in 1882, was
found to be suffering from the inefficiency of its engineers
and horn the decay of its irrigation works ; but the latter had
not reached the state of ruin, past repair, in which the ancient
structures of Mesopotamia are now found. Still, the country
was in a bad way and going from bad to worse, when those who
were called in to prescribe recognised that, for a country that
was wholly agricultural and whose agriculture was entirely
dependent on irrigation, the one thing needful was efficiency in
its irrigation service. The story of Egypt's recuperation cannot
be told here, but the first twenty years' results which followed the
substitution of efficiency for inefficiency in the control of the Nile
IRRIGATION AND ITS EFFECTS. 7
waters may be enumerated in general terms as follows : — ^The
cotton crop, the modern source of Egypt's wealth, increased
from 3,000,000 to 6,000,000 cwt., or in value from £7,500,000
to £15,000,000 ; the maturing of the maize — the peasant's food
crop — ^was assured by its timely sowing being made a certainty ;
the cost of raising crops was lessened by improved means of
irrigating them ; the cultivable area ' was increased from
5,000,000 to 6,000,000 acres ; the value of land was more than
doubled ; and the system of forced and unpaid labour, with its
attendant abuses, was abohshed. The capital expenditure
which produced these results was about £4,000,000. This
figure does not include the expenditure on the Assuan dam and
other works connected with it, the construction of which came
after the realisation of the benefits enumerated. The further
development of Egj^pt which has resulted from these later
works is covered by the summary given in Note i of
Appendix IV.
The historical record of irrigation in India does not go so far
back as that of Mesopotamia or Egypt. It was about 300 B.C.
that Megasthenes, writing of India, referred to the advantage
of double crops resulting from irrigation, whereas the cunei-
form inscription of Hammurabi, already quoted, furnishes
evidence of the practice of irrigation in Babylonia as far back
as 2200 B.C. ; and the hieroglyphic records of the Pharaohs of
the twelfth dynasty, of date about 2500 B.C., do the same for
Egypt-
But it is modern results which are of present interest from a
practical point of view. As one of the most recent construc-
tions, the Lower Chenab Canal is a noteworthy example.
Mr. R. B. Buckley, in " The Irrigation Works of India," thus
describes the effect of its construction : —
" The tract which it commands, known as the Rechna Doab,
is nearly all Crown land. Before the construction of the canal
it was entirely waste, with an extremely small population,
which was mostly nomad. Some portion of the country was
8 IRRIGATION.
wooded with jungle trees, some was covered with small scrub
camel thorn, and large tracts were absolutely bare, producing
only, on occasions, a brilliant mirage of unbounded sheets of
fictitious water. Such was the country into which 400 miles
of main canals and 1,200 miles of distributaries now distribute
the waters of the Chenab, turning some 2,000,000 acres of
wilderness into sheets of luxuriant crops. . . . About 1,300,000
a.cres of the Crown lands have now been allotted to colonists,
and a new population of a million people have founded home-
steads which they cultivate with the waters of the Chenab
Canal."
Considering India as a whole, the result of the work done by
the engineers of the British Government during the past sixty
years is an increase of the area watered by Government irriga-
tion works from 3,000,000 or 4,000,000 to 26,000,000 acres,
brought about by a capital expenditure of 7,124 lakhs of
rupees, on which the net profit amounts to 8 8 per cent. This
takes no account of the indirect profits. The value of the
crops raised is estimated at 9,198 lakhs of rupees, or 138 per
cent, of the capital expenditure on the canals by which they
are irrigated. But this must not all be written down to the
credit of irrigation, as the crops in India, in most cases, are
not entirely dependent on canal water, as they are in Egypt,
and, except in years of drought, there would not be total failure
of the crops, even if the canal supply were entirely cut off. It
is generally reckoned in India that irrigation increases the gross
outturn by about 30 per cent. The Lower Chenab Canal is an
exceptional case in which, perhaps, the whole yield, or almost
the whole, may be credited to the canal.^ Exception also has
already been made of years of drought. A canal system serving
a tract which is severely affected by a serious deficiency in the
rainfall may in a single year save crops equal in value to its
entire capital cost.
The result of irrigation in the United States is thus described
by Mr. Elwood Mead in his paper read at the International
^ See Note 2, Appendix IV,
IRRIGATION AND ITS EFFECTS. 9
Engineering Congress of 1904 : " Since 1900 the arid region
has enjoyed great prosperity. There has been an increase in
western settlement, and the values of both land and water have
had rapid and continued advance. Land in the Yakima valley,
Washington, which could have been purchased five years ago
for $15 an acre, now sells for $75 an acre. Land in the
Turlock and Modesto districts, in California, which sold for $20
an acre three years ago, now brings f 60 an acre. Water rights
in Idaho, which in 1894 found no buyers at $10 an acre, now
have prompt sale at f 25 an acre."
In a work entitled " Irrigation in the United States," by
Newell, published in 1902, the following information is given :
The arid regions, which include two-fifths of the area of the
United States, have an average annual rainfall of 20 inches or
less. Of the arid land and semi-arid regions 470,000,000 acres
is grazing land ; but it appears that the actual amount of land
which is irrigable is, as variously estimated, from 60,000,000 to
100,000,000 acres — a field for irrigation of extent sufficient at
least to satisfy the present generation. The arid regions
extend, moreover, southward into Mexico and northward into
Canada, so that in these two countries also there is ample
scope for irrigation engineering. Mr. Newell states that
twenty to thirty acres of open range in the arid regions is
generally considered sufficient for the support of a cow, and
that the same land under irrigation will feed ten cows. This
agrees with the experience in England, where rain takes the
place of irrigation, the association of three acres and a cow
being familiar to politicians as well as farmers. Mr. Newell
further states that " the open range may have a value of 50
cents an acre, while under irrigation the selling price may
rise to $50 per acre, or even $500 per acre when in orchard."
In a paper on " Irrigation in the Transvaal," by M. R.
Collins, pubhshed during 1906 in Vol. CLXV. of the Pro-
ceedings of the Institution of Civil Engineers, it is stated, with
reference to the value of land in the Transvaal, that " a libera]
lO IRRIGATION.
estimate of the value of good unirrigated land would bfe £^ to
£5 per acre. Each acre of land is enhanced in value by £2$
by being brought under irrigation."
In Europe the countries that practise irrigation are France,
Italy and Spain.
In Northern and Central France irrigation is not a necessity
for raising crops, but it is, all the same, taken advantage of to
increase the fertility of meadow lands for haiy crops. The
prosperity of Normandy, for instance, is due to regular irriga-
tion. In Southern France, however, where the summers are
very dry and hot, irrigation is useful, if not indispensable, for
all kinds of cultivation, particularly meadows. Market garden-
ing is impossible without it. It has been estimated that
irrigation in France brings an increase in net earnings of at
least 200 francs per hectare (^3 7s. dd. per acre). Sir Colin
Scott-Moncrieff states, in " Irrigation in Southern Europe," 1868,
that " in Vaucluse, in the south of France, the rental of good
land not entitled to irrigation is about 3^3 4s., and, if it can
procure it, it rises to about ^^4 3s. per acre " ; and further adds
that irrigation causes an increase of 50 per cent, in the price of
land.
Italy is the country of irrigation in its most advanced stage
of development. The plains of Piedmont and Lombardy pro-
vide material for the liberal education of an irrigation engineer,
and show what artificial control of the natural water supplies
of a country, in competent hands, is capable of effecting.
Lastly, there is Spain. As Italy owes much of its irrigation
laws and customs to the ancient Romans, so is Spain indebted
to the Moors. Valencia, Murcia and Granada, Elche and
Lorca, had Moors for their first irrigation engineers, whose
works remain, active and beneficent, in the hands of the
conquerors who expelled the enterprising race that constructed
them. The irrigation works of Valencia are supposed to have
been executed about a.d. 800. For nearly three hundred years
after the final expulsion of the Moors from their last stronghold
IRRIGATION AND ITS EFFECTS. II
of Granada little was done by the Spaniards to extend the area
of irrigation. But during the reign of Charles III., a.d. 1785
to 1791, dams were built for the storage of water and a fresh
impulse given to irrigation. The dams of Spain vary in height
from 21 to 48 metres (69 to 157 feet).
The result of irrigation in Spaih on land values is remarkable.^
From certified copies of sales during the year 1859 the following
appears: The average price of irrigated ground at Castellon
was £140 per acre, the average price of the ground without
irrigation in the same neighbourhood being ;^io. In Murcia
the price of irrigated land was ;f 500 per acre, of ground without
irrigation £25 to £30. Near Madrid irrigated land was leased
for £5 an acre, while unirrigated land could be bought outright
for that figure. As a rule, for the whole of Spain, good land
without irrigation in the valleys could be bought at an average
price of from £6 to ;^io, and the same land irrigated at £80 to
£120 per acre.
It is thus abundantly evident that, where rainfall is deficient
or capricious, but the soil is cultivable, irrigation is a most
potent agent for converting land, of little value without it, into
valuable property; that a well-administered system of irrigation
may double the value of property that has hitherto been served
by a badly managed system ; and that in a country dependent
on irrigation, the neglect to maintain its canal works in a state
of efficiency will result in its impoverishment and ultimate
ruin.
' Proceedings of Inst. C.E., " Irrigation in Spain," by Higgin (1869).
CHAPTER II.
BASIN IRRIGATION.
The earliest form of irrigation was probably a natural one,
brought about by rivers overflowing their banks during seasons
of flood. Egypt, on the Nile, and Mesopotamia, on the Tigris and
Euphrates, have already been cited as countries in which the
genesis of irrigation was probably of such a kind- Sind, on the
Indus in India, is another notable instance. Most rivers with
periodical flood seasons have their sources in mountain ranges,
where the rainfall is heavy and the ground is rocky. In such
cases the declivity of a river is, at first, very great, and the
velocity of the stream is torrential. The detritus, which is
washed down from the steep slopes of the hills and eroded from
the bed, is carried forward to the point beyond the foot of the
hills where the slope of the stream becomes reduced. Here
erosion ceases and deposition of the heavier detritus commences.
Fan-shaped layers of deposits spread themselves out, and, in
process of time, force the stream to take a new course. Again
the depositing process is repeated until the general country
level is raised. At length the stream cuts a way through its
own deposits down, perhaps, to bed-rock, and flows forward in a
deep channel through the softer plains. Gradually the velocity
becomes less rapid and the channel less deep as the water
flows seawards, until at length the river enters the region where
it overflows its banks in flood.
From that point onwards the bed of the river and the lands
alongside are being gradually raised by the material brought
down by the water, while the delta of the river is being con-
stantly added to along jts seaward margin by the deposit of the
BASIN IRRIGATION. 1 3
annual flood. When the river tops its natural banks and the
flood waters leave its channel, the velocity of flow of the escap-
ing water rapidly diminishes, and, in consequence, the silt in
suspension is deposited in greatest quantity within a short
distance from the river edge ; so that, in course of time, the
lands assume a downward slope away from the river. This is
the explanation of the fact that, in the case of wide flat valleys
traversed by rivers with a periodical overflow, the highest land
is found along the river edge. If there are several branches
traversing a level delta, the surface slope will be away from,
each until it meets the slope formed under the influence of the
adjacent channel. Along the meeting line an escape channel
will probably be formed by the flow-off of the flood waters,
which takes place when the river falls. The delta of Egypt
and the deltas of India furnish examples of this formation, the
further development of which has been arrested by the con-
struction of protective banks to guard the irrigated crops from
being damaged by flood. The Nile valley of Upper Egypt
exhibits this characteristic in its simplest form. The single
channel of the river traverses the valley, and its floods spread
sideways over the land on either side of it. There is thus
formed a land surface of the form shown to an exaggerated
scale in Fig. I. In such a valley as that of the Nile in Upper
Egypt the flood waters of an inundation, if uncontrolled by
artificial works, would move forwards over the land as a shallow
sheet of water with its surface lower than the river level opposite,
and only partially submerging the land. In very extreme floods,
however, the level of the inundation would be everywhere the
same as that of the river alongside. There would be certain
lengths of the high margins of the river lower than other parts,
and, over these, ordinary floods would find their way to the lower
land beyond ; but the highest floods would overtop the river
margin everywhere. A low flood would probably not find its
way to the low land at all, except in small quantity through
natural channels formed by the waters of previous high floods
14 IRRIGATION
cutting their way back to the river. The first thing that would
occur to the inhabitants as a method of securing an inundation,
whether the flood were low or high, would be to make cuts
through the high land along the river edge, whereby water
would be admitted to the more remote lands below flood level.
They would then endeavour to make the water rise over the
higher lands by placing obstructions in the way of the forward
INUNDATION DIAGRAMS
FIG 1
JVatu ra I •-. >s) .
s
1^
flow of the water thus introduced to the lower lands. By some
such process as this, short inundation canals and cross embank-
ments would come into being. Then, to prevent the cross
embankments from being swept away by the effects of a high
flood, a protective bank along the river edge, to exclude excess,
would be felt to be a necessity. ^
But with such arrangements the inundation of the com-
paratively high land near the river would have been a constant
BASIN IRRIGATION.
15
difficulty, necessitating inconveniently high cross embankments
to hold the water up sufficiently. On this account the advan-
tage of separating this width from the remainder, and of
providing for its irrigation by independent canals, would have
suggested itself. For this purpose a longitudinal bank would
be made along the line where the comparatively steep slope
near the river changes to the flatter slope of the more remote
land. The strip alongside the river, thus separated from the
lower lands, would be given its own canal, in which the water
would be held up to the maximum level that the flood in the
iMPERFECT BASfN SYSTEM
i 4
river could produce. The result, in a favourable flood, would
be as shown iri Fig. 2.
In the chain of basins along the lower land arrangements
would have to be made to pass on the water from basin to basin.
At first this would be done by means of openings (by washes) at
the ends of the banks on the higher ground, protected probably
by loose stone Cuts would be made in the banks, along the
line of flow-off in the lowest land, when it was desired to finally
get rid of the water. These cuts would later on be replaced by
masonry regulators and escapes to give better control. There
would thus be created a system of basins arranged as in Fig. 3.
This figure will serve to illustrate the defects of the arrange-
ments when the basin system had reached this stage of evolution.
l6 IRRIGATION.
Y, Y, Y are the main basins of a chain ; X the terminal
basin of the next chain above ; Z the initial basin of the chain
next below the Y chain. The smaller basins y, y, y are
those which include the high margin of the river. The main
basin-feeder discharges into the first basin Y, from which the
water is passed oh to the other basins in succession. The level
in each basin is so regulated by the escapes in the cross
embankments that the water may cover the highest land ; and
thus a succession of water terraces is formed. The escape E
at the tail of the chain passes any excess there may be back
into the river and provides for the final emptying. The
smaller basins y, y, y are worked in a similar way.
Now, in arranging for the supply of water to a basin system,
there are two important principles to be observed. The first
is that, in a year of low flood, the supply should be delivered in
such quantity and at such levels that the whole of the land
may be submerged during the period of flood to the extent that
saturates it sufficiently to secure that the crop, which will be
sown after the flood, shall germinate and come to maturity
without further irrigation. The second principle is that full
advantage should be taken of a good flood to enrich the soil by
encouraging the deposit of the fertilising matter which the river
brings down in suspension from its sources; and that this
deposit should not only be as abundant as possible, but
should be evenly distributed over the whole area of the chain of
basins.
In the scheme depicted in Fig. 3 these two principles are not
observed. The chain of basins Y, Y might perhaps in a low
flood get filled by water passed on from X ; but the case of the
smaller basins y, y would be hopeless without a syphon con-
necting the high-level canal with the upper system X, as shown
by the dotted line.
The second principle enunciated, concerning the distribution
of muddy flood water, has next to be considered. It is con-
ceivable that the high-level canal will satisfy this principle in a
fiASiN IRRIGATION.
17
high flood ; in a low flood, without a syphon connection with
the upper chain, it will not flow at all. But the main basin-
feeder is altogether out of order. It discharges into the first
basin from a channel without banks, and creates a shallow lake
from which the second basin is fed through the cross embank-
ment. In the same way the third is fed from the second, the
fourth from the third, and so on. Consequently the first basin
gets most of the muddy deposit and the lowest basin the least.
An arrangement of canals and banks in a basin chain, which
pays due regard to the principles laid down, is shown in Fig. 4,
IMPROVED BASIN SYSTEM
The main basin-feeder, instead of discharging into the first
basin, passes by it between banks, and is carried, approximately,
along the same alignment as the bank of Fig. 3 which separates
the high and low basins. At the upper corner of each basin is
a feeder-sluice to fill the basin and give it muddy water, so that
all may get a fair share of the fertilising matter. The masonry
works situated in the banks of the basins, at the points where
they cross the natural drainage line, serve to regulate the basin
levels and to empty the basins at the proper time; also to
connect one chain with the next one above and below, so that
water can be passed from one chain to another when it is
advantageous to do so.
I.
1 8 IRRIGATION.
By means of the syphon canal, high level water, derived from
a point on the river at a considerable distance up-stream, is
furnished to the lands beyond the basin-feeder, which, without
it, would be dry in low flood years. Though this arrangement
secures water to the high level tract, the old direct heads from
the river should not be suppressed, as in high floods it is of
advantage to admit a supply through them on account of the
increase of fertilising deposit' to be obtained by so doing. All
the old direct feeders of short run should be maintained with
the object of so using them that full advantage may be taken of
high floods when they come.
If a chain of basins can be linked up with the chain next
above it, the canals of the upper chain can be so disposed and
designed as to effect the inundation of all the lands as far down
as the point where the water of the main feeder of the lower
chain comes to country surface. But, if a chain of basins is in
the unfortunate position of having no chain above it, there will
be land on either side of its main feeder, from its off-take on
the river to the point where its water comes to country surface,
which cannot be flooded. In high floods the unflooded area
may be little or nothing ; in low floods it may be considerable.
The selection of the points at which the main feeders take
off depends on the windings of the river and the configuration
of the land to be irrigated. The position of the off-take on the
river has a great influence on the silting tendencies of the canal.
The original constructors of the inundation canals of India
found that it was best to take off at points screened from the
full force of the current, and, therefore, preferred as a site for
the head of an inundation canal a point on a side branch of
the river some little distance above its lower junction with the
main stream. The soundness of this practice is confirmed by
^he case of a canal in Egypt, the Abu Bagara, which takes off
a side branch of the Nile near its lower end, and is the only old
inundation canal in Egypt which does not silt. The principles
formerly followed by the Arab engineers in Egypt (as stated by
BASIN IRRIGATION. I9
Colonel J. C. Ross in " Notes on the Distribution of Water,
and the Maintenance of Works in Upper Egypt. Cairo, 1892 ")
are opposed to the original Indian practice, being as follows :
" The off-take should be placed in the bank along which the
deep water of the Nile flowed." This rule is stated in a form
as if for guidance, but it lays down a misleading principle. If
the Arab engineers are correctly credited with the observance
of this principle, it does not follow that they are worthy of
imitation, for neither theory nor experience lend their support
to the soundness of this practice. Theoretically the most
favourable place to select for the off-take is any point past
which the river flows with the same velocity as the canal will
flow after the water is drawn into it, so that there may be no
change of velocity. If the canal has its off-take so situated,
there should be a minimum of silt deposit in the canal con-
sistently with a maximum of silt carried forward in suspension
to the fields.^ The question of silt deposit will be discussed in
a future chapter, when it will be shown that one of the condi-
tions of bringing about a diminution of silt deposit in a canal
is an absence of high velocity in the river at the point of off-
take.
The site of the off-take having been decided upon, the slope
of the land surface determines the water surface slope to be
adopted in the feeder canal. Supposing the land on the align-
ment of the canal to have a slope of jj^hrrs' the canal water
surface slope might be ^uitra- The statistics of previous floods
must be studied to determine the duration of the flood and its
levels. In order that the inundation may not fail in bad years,
the project should be based on the levels of a low flood, and on
the period during which the canals would flow to effect the
filling of the basins ; remembering that, even if^ the river levels
admitted of it, the filling cannot be prolonged beyond a certain
da:te, as the basins must be emptied and the land surface be
prepared to receive the seed of the coming crop before it is too
late for the sowing. In Egypt fifty days is the full period of
* See Note 3, Appendix iV.
20 IRRIGATION.
filling. The mean flood level of this period is, for example,
I "50 metres (or, say, 5 feet) below the country surface at the
point where the canal takes off from the river. If, then, the
country slope is xjy^n^, and the canal water surface slope
U(T05i5) the water will come to land surface at a point thirty
kilometres (19 miles) from the canal head, as shown in Fig. 5.
Down to this point, then, the canals of the upper system (if
there is one) must be carried, and the land must be considered
as belonging to the upper chain for the purpose of calculating
the dimensions of canals.
The bed level of the feeder canal should be fixed at that level
below the average level of the flow period which will give the
FLOOD CANAL DIAGRAM
discharge required with a channel of a convenient bed width.
By the " average level of the flow period " is meant the mean of
the levels of the flood at the canal head between the date that
water is admitted into the canal to feed the basins and the date
when the head is closed to shut off the supply. To determine
what the dimensions of the canal should be, a calculation must
be made of the quantity of water required to fill the basms
depending on the feeder, lying between the point where the
water comes to country surface and the point where the water
of the canal in 'the chain next below does the same. The
inundation should be of such proportions that the highest
ground in any basin would be covered by a depth of at least
30 centimetres (i foot) of water. The basins of Egypt vary in
size from 3,000 to 50,000 acres ; the mean depth of the inunda-
tion varies from f metre (2J feet) in small basins to i| metres
(4I feet) in large basins. But, as a rough estimate, sufficiently
BASIN IRRIGATION. 21
correct when we are dealing with principles, 5,000 cubic metres
(176,000 cubic feet) may be taken as the quantity required per
acre of land to be flooded, inclusive of the quantity required to
make good the loss by evaporation and absorption during the
period of inundation. The daily discharge of the main feeder
for the fifty days' period of flow must, therefore, be ^^jth of
5,000 cubic metres, or 100 cubic metres, per acre to be flooded.
The mean flood level of the fifty days' period, used as one of
the data in the designing of the canal, need not be that of an
extreme low flood such as comes but rarely, as in such years a
diminished quantity of water must be made to do increased
duty by bringing each basin in succession up to full inundation
level with the discharge of the basin next above in order.
The bed level and width of the feeder canal can then be
determined with these data, namely, the mean flood level, the
daily discharge, and the water surface slope in the canal.
To deal satisfactorily with the large bodies of water that
have to be distributed over the extensive areas of a chain of
basins perfect control over the water at all points is necessary.
This is only to be obtained by a complete system of regu-
lating works, such as head sluices, to draw the water from
the river into the feeder canal ; basin sluices, to admit
water from the canal into the basins ; regulators in the basin
cross banks to pass on the water and regulate the level in the
basins above them ; and escapes to discharge the water back
into the river.
If the head sluice of the feeder canal is built near the river
edge, it may be in danger from river erosion : for this reason it
is generally placed at some little distance from it, in spite of
the objection that the channel up stream of the head silts up
badly when the head is closed. It is sometimes constructed
on the top of the syphon which carries the water of the upper
chain under the main feeder. Such an arrangement has this
to recommend it, that the head sluice can be so designed that
its weight may resist the tendency of the syphon to blow up
22 IRRIGATION.
when it is working under a head ; but it has the disadvantage
that the design is necessarily complicated, and it is difficult to
arrange for the traffic which passes across the canal and along
its banks.
Again, the head may be built at such a distance down stream
of the syphon as to allow room for a basin escape to be built
between the two. The basin chain would then empty itself by
the escape into the off-take channel of the feeder canal, by
which, if the head sluice openings were closed, the discharged
water would find its way into the river. This arrangement is
shown at F in Fig. 4.
At the tail end of the chain of basins the main escape may
be either situated as just described (F, Fig. 4), or may be
placed in the position of the escape from basin X (Fig. 4) . This
latter arrangement is of the natvure of a level-crossing over the
canal leading to the syphon. In the left bank of the syphon
canal an inlet regulator passes the basin water into the canal,
and an escape in the opposite bank discharges it into the river.
The syphon down stream of the level-crossing is fitted with
regulating apparatus, so that the syphon canal can be wholly or
partially closed at will.
The discharging capacity of the main escape has next to be
considered. The quantity of water to be finaJly discharged at the,
tail of a chain will be the volume contained in the basins, and will
be. less than the estimated quantity required for the filling by the
amount allowedfor evaporation and absorption. For rough calcu-
lations it has been the custom in Egypt to estimate the quantity to
be discharged at the rate of 4,000 cubic metres (141,000 cubic feet)
an acre, which allows nearly a metre (or 3 feet) as the mean
depth of the inundation. But, as the water must be got rid of
in time for the sowing of the saturated ground, a period of
only about twenty days can be allowed for the emptying,
against fifty days for the filling, and, therefore, the tail escape
must be designed to effect the discharge in the shorter period.
The discharging power of the escape, which depends on the river
levels at the time of discharge, will be greater when the river
BASIN IRRIGATION. 23
is low than when it is high ; whence it happens that in good
floods, at any rate if they are late in falling, the escapes work
slowest when there is most water to be got rid of. The escape
should, therefore, be given ample water-way, so that it may
prove sufficient under adverse conditions. It should also be
given an extended apron and ample protection of well revetted
slopes and talus of heavy pitching down stream, as, in the
opposite case of a low river, the escape will have to work for a
prolonged period under the severe conditions of a considerable
head. This same precaution must be taken in the case of the
regulators in the cross-embankments of the basins, as they
discharge into wide expanses requiring an enormous volume of
water to affect the surface level, so that the head remains
undiminished. In other respects the design of such works
may be the same as that of ordinary regulators ; the volume of
water to be passed, the time to be allowed for passing it, and
the head under which the discharge will be effected determining
the water-way to be allowed in each case.
The programme of operations in the filling and emptying of
a chain of basins is, in general terms, somewhat as follows : —
On a fixed date (generally August loth in Upper Egypt) the
basin feeder heads are opened, and the basins commence to fill.
The escapes are likewise opened so as to admit river water also
by them into those basins which are in connection with the
escape channels ; but, as soon as the water coming from above
causes a reverse flow back into the river, the escapes are closed
again. The basin-filling by the feeder canal continues at a rate
depending on the river levels. At the same time, water is passed
forward into the canals overlapping the feeder of the next chain.
One of the principles laid down for observance in the
designing and working of a basin system is that full advantage
should be taken of a good flood to obtain the maximum deposit
of fertilising matter possible ; and one way of doing this is to
pass as much water as possible through the basins. To effect
this, th6 head sluice of the feeder canal should not be closed
24 IRRIGATION.
when the basins are full, but should be left open, and the levels
in the basins regulated by the opening of their escapes to the
necessary extent. In this way a quantity of water is admitted
to the basins in excess of that required to fill them, and, as the
current in the wide expanse of water is imperceptible, a larger
volume of silt is deposited and the land therefore derives greater
benefit.
In fifty days after the first admission of water, or less if the
flood is a good one, all the basin land should be under water ;
and a week later (October 5th) the basins should be ready to
discharge. The feeder heads are then shut down, and the
supply from the river cut off ; the upper basins are discharged
on to the lower to complete their inundation, if still incomplete,
and the water passed forward from basin to basin to the tail of
the chain, where it is finally got rid of through the escape into
the river. In a fortnight or three weeks the basins should be
empty, with the exception of the water in the lowest hollows
which drains off more slowly. The seed of the basin crop
— wheat, beans or clover — is then scattered broadcast over the
surface ooze and merely pressed into it by a plank drawn over
the ground ; or else, after a short interval of drying, the land is
lightly scratched with a plough before the seed is scattered. The
crop is then left to take care of itself till it is ripe for harvest.
Before leaving the subject of basin irrigation it may be useful
to note the dimensions of the basin banks adopted of late years
in Egypt. The principal basin banks, and the river bank, have
a crest width of 5 metres (16 feet) and side slopes of 2 of base to
I of rise. The crest level is made ij metres (4 feet) above
highest water level. The slopes exposed to wave action on the
side of the prevailing wind are, in the completely remodelled
banks, protected by dry rubble pitching to heights varying with
the intensity of the wave action ; or else by a dwarf masonry
wall where the action is too severe for dry rubble to resist. In
the case of banks exposed to water on one side only, the
unexposed slope is made with a base of 1^ to a rise of i.
BASIN IRRIGATION. 25
The crest width of the less important banks of small height
varies between 3 and 4 metres (10 and 13 feet), and the crest
level is a few inches lower, with reference to the high water
level, than in the case of the more important banks.
In India, the area of cultivation dependent on inundation
canals, maintained by Government, is about 4,000,000 acres.
There is, in addition, land irrigated by canals belonging to private
owners, and by other canals belonging to a native State.
The chief inundation canals of India are to be found in the
basin of the Indus and its five tributaries. The almost rainless
district of Multan is rendered abundantly fertile by a series of
inundation canals fed by the Sutlej and the Chenab on either
side of it. Sind, also nearly rainless, raises crops of over
1,500,000 to 2,000,000 acres by means of the irrigation provided
by 6,000 miles of inundation canals. In one respect the inun-
dation canals of the Punjab in India differ widely from those of
Egypt. The latter have a bed slope of aoSoo '> while the canals
of the Punjab have sometimes as steep a gradient as j^^, and
rarely less than r^hsa- This difference is due to the fact that
the slope of the country is much steeper in the Punjab than it
is in Egypt. Consequently the flood water of the Punjab rivers
can be brought to soil surface after a much shorter run in the
canal than is possible in Egypt.
There is one other respect in which the inundation system of
India differs from that of Egypt. In Sind and the Punjab in
India a large proportion of the work done by the inundation
canals is in the irrigation of the kharif crops — ^jowar, bajra and
rice. These crops are irrigated during the flood season by the
inundation canals in the ordinary way, that is, by field channels
fed " free-flow " from the canals, as distinguished from a system
of inundation. But for the rahi, or cold weather crop of wheat
(chiefly), the fallow land is inundated by the flood water with
the same object as in Egypt, namely, to manure the surface of
the ground with a layer of silt deposit, and to saturate it
26 IRRIGATION.
sufficiently for the needs of the winter crop. In Sind the rabi
area so inundated bears only a small proportion to the whole
area irrigated from the inundation canals; whereas in Egypt
almost the whole of the flood irrigation consists of the inun-
dation preparatory to the sowing of the winter crops — wheat,
beans and clover. There is a comparatively small area of
millet, raised by flow from the flood canals of Egypt, which
corresponds to the flood irrigation of kharif crops in India. It
would, therefore, seem more correct to call such canals in India
flood canals; masmuch as they irrigate in the ordinary way
during the flood, and inundate to a less extent ; whereas the
basin canals of Egypt are true inundation canals, as the
ordinary irrigation of millet done by them is insignificant in
amount in comparison with that effected by inundation.
There is no basin system in India, properly so called, such as
there is in Egypt. The inundation canals of India work
independently of one another, without connection or over-
lapping of spheres of influence, so that there is no opportunity
afforded for correcting the shortcomings of a low flood by
leading water from a higher system into a lower one.
It is interesting to find that the principle of the basin system
of Egypt has been adopted by the fanners of the North
Western Plateau of Cape Colony in South Africa. Their
practice is thus described in a report written by Mr. W. B.
Gordon as Director of Irrigation of Cape Colony.
" The most successful works in this tract are undoubtedly
those which have been constructed by the farmers themselves,
for the utilisation of the intermittent flood waters on the
flat lands or ' vleis ' adjoining the rivers, more especially the
Zak river, along which these vleis are especially numerous.
The water is diverted from the river by means of a cheap
masonry weir, or, where rock is not available, by means of
an earthen dam constructed bank-high across the river and
washed away by every moderate flood. Sluit channels, or
BASIN IRRIGATION. 2/
' furrows ' as they are called, convey the water on to the lands
where it is held up to a maximum depth of three to five feet by
small banks or ' saai ' (i.e. sowing) dams constructed across the
vlei. When the sowing time arrives, the impounded water is
let off to moisten the lands below the dam, and these, together
with the saturated lands above, are then ploughed and sown."
CHAPTER III.
PERENNIAL IRRIGATION AND WATER "DUTY."
Under the basin system, described in the last chapter, only
one crop can be raised during the year, and that only a winter
crop of cereals or beans. The more valuable summer crops
cannot be grown. These latter require periodical waterings
when the river is low, and protection from inundation when
the river is high. The system of irrigation under which such
crops can be matured is known as "perennial," the water
supply being continuous throughout the year. When such a
supply is obtainable for irrigation, an average of two crops a
year can be grown, provided that the water carries fertilising
matter to the fields or manure is freely used. The mean
value of a perennially irrigated crop is greater than the
value of a single basin crop of wheat or beans. Hence
it follows that, as two crops a year, are raised under the
perennial system and only one under the basin system, the
value of the crops in the former case is more than double
that in the latter, which accounts for the fact that both the
selling and renting value of perennially irrigated land is more
than double that of basin land. The preference for perennial
irrigation, wherever it is possible, is, therefore, quite natural.
One of the results of the building of the Assuan dam on the
Nile, and of the storage of water above it for use in the summer
months, has been the conversion of 450,000 acres of basin land
into land under perennial irrigation. This is the most modern
instance of the development of perennial irrigation at the
expense of the flood system.
The earliest definite record of perennial irrigation has already
been given in the first chapter. Hammurabi, who ruled in
Babylonia about four thousand years ago, must be accepted as
PERENNIAL IRRIGATION AND WATER "DUTY. 29
the oldest known constructor of perennial canals. But, though
it has been assumed that Egypt under the Pharaohs owed
her prosperity to the basin system of irrigation, and that
perennial irrigation was not introduced into Egypt till quite
recently, in Mehemet All's time, it is by no means improbable
that the extreme north of the Delta enjoyed perennial irrigation
in Ptolemaic and Roman times, and had enjoyed it possibly
for centuries before Hammurabi dug his Grand Canal of
Babylon. For, two thousand years ago, there was still in
working order a remarkable natural reservoir in connection with
the Nile, known as Lake Moeris. According to Herodotus, who
visited the lake about 454 B.C., the Nile water flowed into it half
the year, and flowed back again to the river during the other
half. Strabo and Diodorus Siculus both state that the reservoir
was still in action nearly five hundred years later. Somehow,
and at some time since then. Lake Mceris disappeared, but the
cultivated lands of the modern province of the Fayum have
been identified as the bed of the ancient lake, and the low-
lying Lake Kurun as the persistent rudiment of the reservoir.
The existence of such a reservoir as Herodotus describes would,
it is reasonable to suppose, have created conditions of flow in
the deltaic branches of the river favourable to the working of a
system of perennial irrigation in the lowlands of the north
bordering the Mediterranean, provided only that the land level
had been in those days higher than it is now with reference to
sea level ; and convincing evidence exists that it was so.
There is also evidence to show that this land, now a barren
plain, was cultivated in the past and densely populated.
Numerous mounds strewn with bricks and pottery mark the
sites of former towns and villages, and Rameses the Great and
other Pharaohs held their courts on the Tanitic branch of the
Nile at Zoan, or Tanis (now San-el-Hagar, a fishing village of
the waste).
In India, the Madras native engineers introduced the system
of perennial irrigation long before the East India Company
30 IRRIGATION.
was formed. A weir across the Cauvery river in Madras, which
is called the Grand Anient, is said to have been constructed
one thousand six hundred years ago — a modern work compared
to the canal of Hammurabi and Lake Moeris, but still ancient
enough to discourage the present generation from claiming
perennial irrigation as a modern innovation ; though it is
modern in this sense, that it is the system which is now
adopted in all new irrigation projects.
With reference to this point, Mr. El wood Mead,* in his
paper, already quoted, remarks : " Although modern irrigation
in the United States only dates back fifty years, its practice on
this continent is older than historical records. The first
Spanish explorers on the Rio Grande found the Indians of that
valley watering the thirsty soil, as their forefathers had done
for unnumbered generations before them, and as their descen-
dants are doing to-day. In Southern Colorado and Northern
Arizona and New Mexico are well-defined remains of irrigation
works, of whose origin even tradition is silent."
With this much of historical introduction, attention will now
be directed to the study of the methods of perennial irrigation.
There are three periods into which the evolution of a canal
scheme may be divided, namely : the drawing up of the project,
the construction of the works, and the utilisation of the works
for the purpose for which they are constructed. These subjects
will be taken in order, and the various points connected with
each considered.
The project has naturally to be prepared first. Suppose,
then, that for the sake of preventing famine or scarcity, or of
promoting the prosperity of a country, it has been decided to
resort to irrigation, and that the irrigation engineer has been
called upon to prepare a project. He will first of all study the
climatic conditions of the country to be irrigated, and the
existing nature of its agriculture ; he will then examine the soil
> Paper No. 33, " Irrigation in the United States," by Elwood Mead,
International Engineering Congress (1904).
PERENNIAL IRRIGATION AND WATER " DUTY." 31
to determine what crops it is capable of bearing under the
stimulus of artificial irrigation, and he will make himself
acquainted with the configuration of the land, so as to form a
general idea of the scheme of canals and drains to be elaborated
afterwards.
The rainfall, as one of the climatic conditions to be studied
at this preliminary stage, is that, of the region which is to be
irrigated, and not of the catchment area from which the water
supply for the irrigation is to be derived. This latter will form
the subject of later study, when it becomes necessary to con-
sider the available sources of water supply. What the engineer
entrusted with the preparation of the project first requires
to know is, when and in what quantity rain falls on the area to
be cultivated, with the view of ascertaining to what extent the
rainfall requires supplementing by irrigation. And it is not
only the deficiency of the rainfall that must be taken note of,
but also its capriciousness ; for it is when the climatic con-
ditions affecting agriculture are at their worst that irrigation
should prove itself a reliable insurance against loss of crops.
Rainfall statistics, so far as they exist, must therefore be
collected. Statistics of temperature are also necessary, as
temperature is a factor regulating the intensity of the demand
for water and affecting the available supply through evapora-
tion. The quality of the soil is another factor of similar
influence : light sandy soils require more water than heavy or
clay soils, and the loss of water by absorption is greater with
the former than the latter.
There is an important matter affecting the calculations to be
made that should receive attention from the very first, as a
preliminary step. If the source of supply is to be a river, and
reliable records of its rise and fall and discharges do not exist,
gauges should be at once set up and regular readings taken,
while the discharges of the river should be measured at regular
intervals, and the observations continued during the period of
study, to furnish data, if no better exist, upon which calculations
32 IRRIGATION.
can be based. The same should be done if the source is a lake :
its levels should be regularly observed, and the discharge of its
in-flow, or outlet channel, or both, regularly measured.
The preliminary studies indicated in the foregoing remarks
relate to the demand for water. Their purpose is to furnish
data upon which to base an estimate of the quantity of water
required for the irrigation of the total area to be brought under
cultivation. To make this estimate, we must determine the
" duty " of water under the conditions of climate, soil, crops,
and methods of distribution which exist, or will exist, in the
tract to be irrigated. _
The " duty " of water is a technical term used by irrigation
engineers to signify sometimes the amount of work that water
may be expected or ought to do in irrigating crops, and some-
times the amount it actually does in any one season. As the
word " duty " implies an obligation, the former signification
would appear to be the more correct, and will be adopted in
this work. The " duty " of water may then be defined as the
measure of the efiicient irrigation work that water can perform,
expressed in terms establishing the relation between the area
of crop brought to maturity and the quantity of water used in
its irrigation. The expression " efficient irrigation work " implies
that the water supplied to the crop is neither more nor less
than what is best for it.
The relation between water and crop can be stated in various
ways according to the unit of measure selected. The " duty "
may be represented as the area of crop matured by a given
quantity of water flowing continuously ; or as the quantity of
continuous flow required to mature a given area of crop ; or
as the total volume required for a given area of crop.
In India the measure of the " duty " is expressed in terms of
that area of crop which a discharge of i cubic foot per second
(abbrev. i cusec), flowing continuously during the life of tht
crop, is able to bring to maturity. This same form of expres-
sion IS also used in America when considering the flow of a
PERENNIAL IRRIGATION AND WATER "DUTY." 33
stream, with, however, "second-foot" as the abbreviation
for I cubic foot a second. But when the contents of a storage
reservoir, for instance, is in question, the " duty " of water is
sometimes expressed in terms of the volume of v\?ater which
will cover an acre to a depth of i foot, and which, therefore,
equals 43,560 cubic feet. This unit of volume is called an "acre-
foot." The storage capacity of a reservoir is given in America
as so many " acre-feet," whereas in India the content would
be given as so many million cubic feet, and in Egypt as so
many million cubic metres. The "acre-foot" unit has this
advantage among some others, that it bears a direct relation to
the unit used in defining areas of cultivation, and it is more
convenient for comparison with rainfall figures which are given
in inches of depth. It is also more suitable than cubic feet
when large volumes have to be represented by figures, as, for
instance, when considering such matters as the annual storage
of the Great Lakes of the St. Lawrence basin, which is
calculated to reach a figure of 2,419,000,000,000 cubic feet.
The relation between the two terms — i cubic foot per
second (cusec, or second-foot) and i acre-foot — is as follows : —
One cubic foot per second flowing for twenty-four hours will
cover an acre nearly 2 feet (I'gS) deep ; that is, it delivers an
amount equal to nearly a acre-feet. If the acre-foot is used as
the term of expression, the "duty" is that number of acre-feet
required to mature an acre of crop.
In Southern Europe the " duty " is stated as so many litres, or
sometimes cubic metres, per second per hectare. In Egypt the
" duty " is similarly expressed in terms of a continuous flow,
namely, as that discharge in cubic metres per day of twenty-
four hours, flowing continuously during the life of the crop,
which is required per acre. It is also sometimes expressed in
the form used in India, with cubic metres substituted for
cubic feet, the " duty " then being the number of acres of crop
which I cubic metre per second, flowing continuously
during the life of the crop, can bring to maturity.
I. o
34 IRRIGATION,
There is yet another unit of quantity used in the United States
West, known as the " miner's inch." It is a little uncertain in
value, as it varies according to the method of measurement. In
California it represents a fiftieth part of a second-foot, in
Arizona a fortieth.
The "duty" of water is said to be a high or a low one
according as a given quantity successfully irrigates a large or a
small area.
The different methods of expressing the " duty " of water
have each points to recommend them, according to the object
of the calculation in which the " duty " forms one of the factors.
Thus, if it is desired to determine the area of crop that a
known discharge can irrigate, it is convenient to have the
"duty" expressed as the area that a continuous discharge of
I cubic foot, or i cubic metre, a second can irrigate. If,
on the other hand, the calculation of the discharge required for
the irrigation of a given area is being worked out, it is more
convenient to have the "duty" expressed in the form most
used in Egypt, namely, as the number of cubic metres required
to irrigate an acre. The acre-foot, it has already been pointed
out, is a convenient form to use in calculations relating to large
storage works.
As the " duty " of water, or the measure of its power of doing
work, is the basis of all calculations in the design of an irrigation
project, it may be well to show by a simple example how the
" duty " may be arrived at. Let it be assumed that the conditions
of climate and soil, and of crop requirements, are such that
waterings are required at intervals of eighteen days, and that
each watering is equal in volume to the quantity represented
by a depth of 3J inches over the land surface. An acre has a
superficial area of 43,560 square feet. Each watering will there-
fore require a quantity of (^ X 43,560 =J 12,705 cubic feet per
acre at the field. If it is desired to calculate the "duty "of
■w ater at the canal head, so as to determine what quantity the main
PERENNIAL IRRIGATION AND WATER "DUTY." 35
canal must draw in from the source of supply, an allowance must
be made for loss of water between the canal head and the field.
What this allowance should be depends upon many things.
The loss is rarely less than 30 per cent., and may even amount
to as much as 70 per cent, when the conditions are unfavourable
to economy. It is due to evaporation and absorption in the
carrying canals and to waste in the fields. The condition of
the canals, and the degree of skill and care applied by both
engineers and cultivators to the distribution of the water, has
great influence on the amount of the loss. Evaporation,
moreover, varies with temperature and with the humidity ol
the atmosphere ; absorption with the soil ; and both with the
distance that the water has to travel between the source and
the crop. The calculations must therefore admit the inevitable
coefficient that varies with the particular conditions of each
case, and so introduce the element of individual judgment
which is so liable to err. However, there is no help for it.
The percentage of loss by absorption is greater in new
canals than in old ones in consequence of the staunching action
of silt deposit both on the bed and slopes. The absorption
naturally bears a direct relation to the extent of the surface of
the bed and slopes with which the water is in contact. Recog-
nising this, the engineers of the Punjab, in India, use this area
as the basis of their estimate of the quantity absorbed, assuming
a loss of 8 cubic feet a second per million square feet of
wetted surface.
From experiments made on the Ganges and Bari Doab
Canals in India, the following conclusions as to the loss of
water from evaporation and absorption in running canals,
between the source of supply and the crop, were arrived at.
Of the volume drawn in at the canal head —
15 to 20 per cent, is lost in the canal ;
6 to 7 per cent. „ „ „ „ distributaries ;
21 to 22 per cent. ,, „ „ „ village water-courses.
It was further held that half of the remainder was wasted in
D 2
36 IRRIGATION.
various ways by the cultivators, mainly in excessive irrigation.
This is evidently somewhat of an assumption, and, in any case,
the figure arrived at by actual experience, as that which
represents the "duty" of water, will cover this waste, if waste
there is. It is not reasonable to expect such economy on large
irrigation systems as is obtainable when each plant is served by
a watering pot.
If the loss between the canal head and the crop is assumed
to amount to 40 per cent, of the discharge entering the canal
head, the estimate of water required is completed as follows,
it having already been found that the quantity required at the
field for a single watering of i acre is 12,703 cubic feet. H
Q is the quantity drawn in at the head, its value will then be
found from the following equation
Q - 1^ Q = 12,705 cubic feet :
whence Q = 21,175 cubic feet.
This is the quantity required per acre of crop once every eight-
teen days ; or, in other words, a continuous discharge at the
canal head of 1,175 cubic feet per day is required for every
acre of crop. This is one way of expressing the " duty."
There is next to be determined the value of the "duty"
expressed in the area irrigated by i cubic foot a second. To
arrive at this, the calculation must be made of the number of
times a discharge of i cubic foot a second, flowing for eighteen
days, will give the quantity required for a single watering of
I acre, namely, 21,175 cubic feet. A discharge of i cubic
foot a second gives 86,400 cubic feet a day, or 1,555^200
cubic feet in eighteen days; and is therefore suflicient to
irrigate
hmim = 73.44 acres.
21,175
Hence, under the conditions assumed, 73*44 acres is the " duty"
of the supply at the canal head.
The results of actual experience will now be given.
In India the " duty " varies considerably, as might be expected
PERENNIAL IRRIGATION AND WATER "DUTY." 37
in a country where the conditions affecting it have so wide a
range of variability. There are two crop seasons in India,
known as the kharif and the rabi. The kkarif season includes
the period of heavy rain, which may be said to extend, generally,
from the middle of June to the middle of October ; the rabi
season is the period of cold weather, November to March. "^ The
crops of the kharif season are, in the United Provinces and the
Punjab, maize, indigo, cotton, and other crops, with a small
proportion only of rice ; in Bengal they are almost entirely rice.
The crop of the rabi season is mainly wheat. As a rough
average it may be reckoned that i cubic foot a second will
irrigate from 140 to 160 acres of rabi crop, and 70 to 80 acres
of kharif.
In Egypt the " duty " has been worked out carefully for the
summer crops only, of which sugar-cane and cotton are the
most important ; and it has been assumed that rice (also a
summer crop) takes double the amount of water that the other
crops do. During the life of these crops no rain falls, so that
they are entirely dependent on the canals for the water necessary
to their growth. As the result of observations made during a
succession of summers of very low supply in the Nile, the
conclusion was arrived at that an allowance of water at the rate
of 30 cubic metres a day per acre of summer crop, and double
that amount for rice, is sufficiently liberal to provide a watering
every eighteen days for cotton, sugar-cane, &c., and every nine
days for rice; or, in other words, i cubic metre per second
is sufficient for 2,880 acres of summer crop, or half that area of
rice. ~This is equivalent to saying that i cubic foot a second
will irrigate 81J acres of summer crop, or half that area of rice.
In Egypt it has been found that 40 per cent, of the gross area
is annually put under summer crop.^ The " duty," above stated,
of 30 cubic metres a day, is per acre of crop ; if this is converted
into the " duty " per acre of gross area, the figure becomes 12
cubic metres. If, then, the area commanded by a canal
• See Note 4, Appendix IV.
38 IRRIGATION.
system — which in Egypt is identical with the gross area — is
e.g., 1,000,000 acres, the discharge required to be drawn into the
main canal from the source of supply is 12,000,000 cubic metres
a day during the hfe of the summer crops.^
In the perennially irrigated tracts of Egypt it is reckoned that
nearly all the land is under crop during the flood season, 40 per
cent, being cotton and the remainder maize. For the flood
season an allowance of 25 cubic metres a day per acre of gross
area is the accepted figure. The levels obtainable in the flood
season being higher than at other times, the increased discharge
can easily be supplied. By a system of distribution that is
favourable to agriculture both in the flood and summer season
(to be described later) the canals are made to carry the summer
and flood discharges with convenient surface levels, though one
is nearly double the other in volume.
As regards the rice crop in India, irrigation engineers have
practically accepted 50 acres at the head of the canal system as
the " duty "for a continuous discharge of i cubic foot a
second, allowing a period of about twelve days for irrigating
the whole area of crop. In Eygpt, when the intervals between
waterings are fixed at nine days, the duty is 42 acres for the
same discharge. If this latter period were to be extended to
eleven days, the " duty " would rise to 51 acres. As the
period in India is given as about twelve days, it may be said
that both India and Egypt are agreed upon this point.
It is interesting to find that the recent experience of irrigation
in India and Egypt has led to the same conclusion as that
reached by Italian engineers fifty years ago. It has been stated
above that in Egypt i cubic foot a second will irrigate 81J
acres of summer crop, or half that area, say 42 acres, of rice.
Now Baird Smith, in " Italian Irrigation," 1855, Vol. II. p. 66,
states that, " According to the best Italian authorities, i cubic
foot per second is sufficient for the irrigation of from 35 to 40
' In this calculation the extra allowance for the comparatively small area
of rice has not been taken into account.
PERENNIAL IRRIGATION AND WATER "DUTY." 39
acres of rice"; and adds, " This is fully twice the quantity
required for ordinary meadow irrigation." He also, when
summing up, comes to the conclusion that, " under ordinary
circumstances, the effective power per cubic foot per second is
93 acres."
Sir Colin Scott-Moncrieff, in his " Irrigation in Southern
Europe," 1868, presents a Table on p. 33 which gives, for the
south of France, a mean " duty " of 83*4 acres, watered during
the six months of irrigation, for a continuous discharge of
I cubic foot per second, with seven to fifteen day intervals
between waterings.
Wilson, in his " Irrigation Engineering," 1903, gives the
following information concerning " duties " in the United
States : — " The State engineer of Colorado now accepts 100
acres per second-foot as the " duty " for that State, varying
on the supply at the head from 70 to 190 acres. In Utah 70
to 300 acres per second-foot is the duty. In Montana it is
about 80 acres per second-foot."
In Southern California the " duty " obtained is very high.
For surface irrigation it is 150 to 300 acres ; for sub-irrigation
from pipes 300 to 500 acres. So high a " duty " is only to be
obtained by the use of cemented channels and pipes for carrying
the water, and probably only in the case of orchard cultivation.
Newell, in " Irrigation," 1902, p. 314, states: " It is frequently
estimated that i cubic foot per second, or second-foot flowing
through an irrigating season of ninety days, will irrigate 100
acres." This, as a rule of thumb, would be a convenient one,
but, in the case of kharif in India and summer crops in Egypt,
70 to 80 acres would seem to more accurately represent the
average " duty."
In a report on the best method of utilising in irrigation the
waters of the River Guadalquivir, made in 1906 by Mr.
R. B. Buckley and the author of this work for the Spanish
Government, the " duty " adopted in the projects recommended
was I cubic metre per second for every 2,000 hectares of winter
40 IRRIGATION.
crop, and for every i,ooo hectares of summer crop. This is
equivalent to a " duty " of 140 acres in winter and 70 acres in
summer for each cubic foot of discharge per second. In the
same report the duration of the irrigating seasons was reckoned
as six months for the winter crop and four months for the
summer crop.
When the engineer entrusted with the preparation of a
project has, after consideration of all the conditions affecting
the question, decided on the " duty" for each crop or season,
and has ascertained the areas under crop in the different
seasons, and the periods for which each crop requires irrigation,
it is then a simple matter to calculate with these data the
discharges required throughout the year, or the quantity of
water that it is necessary to store annually. If it is the con-
tinuous discharge of a canal which it is desired to determine,
the duration of the life of the crop does not affect the calculation.
If, for example, the "duty" for a particular crop or season is
80 acres per cubic foot of discharge per second, the discharge
required for 10,000 acres of crop will be ( — ~— = j 125 cubic
feet a second flowing continuously for the period during which
the crop requires irrigation, whatever that period may be. If,
on the other hand, it is desired to calculate the total volume
of water required to bring a crop to maturity, as may be
necessary in considering the question of storage, the period of
flow is a necessary factor. In India this period is technically
known as the base of the " duty." Taking the same example
as before, if the " duty " is 80 acres per cubic foot per second,
and the area of crop 10,000 acres, and the time during which it
requires irrigation one hundred days, the total volume required to
mature the crop will be f-~ X 86,400 X 100=") 1,080,000,000
cubic feet. In this case the " duty " of the water of the
reservoir may be expressed as 108,000 cubic feet per acre,
PERENNIAL IRRIGATION AND WATER "DUTY.' 4I
implying that, on the average, each volume of 108,000 cubic
feet of water drawn from the reservoir is sufficient to mature
I acre of crop. An addition to the total volume required to
mature the crop must be made to allow for evaporation and
absorption in the reservoir itself, in order to arrive at the total
quantity of storage necessary. In this example it is assumed,
in the first case, that the " duty" used is that at the head of
the canal, and in the second case at the reservoir outlet.
The amount of irrigation work that canal water actually
does — or, rather, is shown in annual reports as doing — varies
from year to year in consequence of the rainfall not being a
constant quantity. The explanation of this is that the canal
water is credited with the work done by the rain. This
accounts for the great variation in the so-called "duty"
(signifying work actually done) which appears in the annual
irrigation reports of India for any particular canal. Taking,
for example, the November figures of the Bari Doab Canal for
ten years, the " duty " (work actually done) of i cubic foot
a second varies from iii to 222 acres, the average being
169 acres. From the statistics of work actually done by water,
the amount of work which it may be expected to do, under
either normal or extreme conditions as may be desired, is
determined. In the particular case of the Bari Doab Canal,
the accepted " duty " for the rabi season, representing the
work that ought to be done, is 160 acres to the cubic foot per
second. The statistics of the month of November were
selected for ascertaining the " duty," as November is the
month in which the rati sowings are principally made, and
the "duty" which can be obtained in that month may
determine the area of crop which can be sown.
Mr. Buckley points out that it is the " duty " of the "period
of pressure," or greatest demand, and not of the whole
irrigating season, which is the important " duty " to determine.
" The ' duty ' of water drawn in at the head of a system is a
42 IRRIGATION.
useful factor in many ways, but it is often most desirable to
gauge it at other points in the system, and with reference to
different ' bases,' that is, to shorter periods of time than that
of the whole irrigating period of a crop ; for the 'duty ' based on
the discharge drawn frqm the source of the supply on the
average of the whole season fails to take cognisance of
fluctuating demands. It is necessary in most cases to know
not only the average discharge of a season, but the maximum
discharge required at a period of pressure during the season."
The summer" duty " of water in Egypt is not calculated from
the whole irrigating period of a crop, but from the period
during which the whole available supply in the Nile is utilised
and it is found necessary to apply rotations to secure a fair
distribution of water. The duration of the latter period varies
from seventy to one hundred days. If any longer period is
used for the calculation of the " duty," such, for instance, as
the life of the crop, the "duty" would appear less than it
should, in consequence of surplus water, that was doing no
work, not being eliminated from the calculations.
Similarly, when rain supplements artificial irrigation, the
" duty " appears higher than it should do, as the watering done
by the rain is credited els work done by the canal water.
CHAPTER IV.
SOURCES OF SUPPLY.
The preceding chapter deals with the considerations that
regulate the demand for irrigation water : the present chapter
relates to the question of supply.
Rainfall is the primary source of all water supplies ; but if
rain does not fall when or where the need of water is felt,
then artificial means must be devised to keep it in hand when
it does fall, till it is wanted, or to carry it to the place where it
is required, unless Nature has undertaken to do both. Rivers
are Nature's waterways which carry the rain-water that falls
in their catchment areas to regions where, may be, no rain
falls. The case of the Nile and Egypt has already been cited
as a well-known example. But the open channels of rivers are
not the only natural carriers, though they do by far the heaviest
part of the work. Water travels also by ways unseen, in closed
channels underground, confined between watertight strata, and
feeds springs and wells, often at great distances from the starting-
point. Such a natural arrangement fulfils both duties ; it not
only provides for carrying the water to the places where it is
used, but for holding it in reserve till it is drawn upon.
This underground supply, when utilised for irrigation, is
tapped chiefly by wells fitted up with some form of lifting
apparatus. From the point of view of agriculturists well-
irrigation is an important matter. It has been estimated that,
of the 44,000,000 acres under irrigation in British India in 1903,
13,000,000 acres were irrigated from wells, of which there were
probably 2,500,000.
In Egypt well-irrigation has less importance, and will have
44 IRRIGATION.
less and less as the canal system becomes more perfect.
There are some 30,000 wells still used for irrigation in Lower
and Upper Egypt.
In California there are about 150,000 acres served by wells, the
artesian conditions of the Californian valley being exceptionally
favourable to this form of irrigation. There are said to be
8,097 artesian wells in the State.
Important though well-irrigation may, therefore, be held to
be as an aid to agriculture, the construction of wells and the
management of the irrigation effected by them are matters
which are not generally considered to lie within the province
of the irrigation engineer. They have hitherto been left to
private enterprise, and the farmer would probably prefer to
have it so. For, as Sir Colin Scott-Moncrieff pointed out in
his Address to the Engineering Section of the British Associa-
tion, 1905, " there is one practical advantage in irrigating with
the water raised from one's own well, or from a river — it is in
the farmer's own hands. He can work his pump and flood his
lands when he thinks best. He is independent of his neigh-
bours, and can have no disputes with them as to when he may
be able to get water and when it may be denied to him." But,
though well-irrigation can be made a profitable farming opera-
tion for any class of crop when carried out by cultivators
who work on the land themselves and use their own cattle, it is
otherwise an expensive method, and can only be made to pay
by cultivating the more valuable kinds of crops. Moreover, it
would seem to be out of favour with those who have had experience
of both canal and well water Mr. Buckley remarks : " The
superiority of the rain-water over that of wells is demonstrated by
the fact that near the heads of the Punjab canals the cultivators
prefer to pay canal rates and to lift the water from the canals
rather than to lift it from wells, although the canal level and
the spring level are about the same." On the other hand,
during the cold weather, well water is given the preference on
account of its higher temperature as compared with canal
SOURCES OF SUPPLY. 45
water. To this day the opium cultivators of Behar, a district
of India, lift water from their wells rather than run it on to
their fields from the canals.
Rivers are the principal sources from which the irrigation
engineer draws the supply of water required to feed a canal
system. Some rivers are fed by rain, others by snow. If they
are fed by rain, the rise and fall of the river will respond to the
rainfall more or less faithfully according to the remoteness and
nature of the catchment area in which the rain falls, if no lakes
intervene to affect the forward flow. If the rivers are fed by
snow falling on mountain heights where their sources lie, the
rise of the river will commence when the summer heat causes
the snow to melt. The snowfields that feed certain rivers
are Nature's reservoirs for the storage of water till the
summer comes. And, moreover, such reservoirs are automatic
in their action, for, the greater the heat, the greater will be the
want of water for irrigatipn, and the more plentiful the
discharge from the melting snow. This convenient arrange-
ment produces conditions favourable to the working of a
system of perennial irrigation. The Indus and other rivers
of Upper India are snow-fed. So, also, is the Tigris ; but,
though the dawn has appeared, Mesopotamia is still waiting
for the rising of a fuUy developed Irrigation Department with a
mandate to take advantage of the gifts that Nature offers and
restore to the Icind of the twin rivers its former prosperity.
There are some rivers which have lakes for their sources, the
lake basins serving as collecting reservoirs for the rain which
falls in their catchment areas. Rivers so fed do not exhibit the
same fluctuation of levels as rivers that have no such collecting
basins to operate as moderators. The largest group of natural
reservoirs in the world are the great lakes of the St. Lawrence
basin above the Niagara Falls, which have a surface area aggre-
gating nearly 88,000 square miles, and a catchment of 265,095
square miles. The mean annual fluctuation of the levels of
these lakes is very nearly i foot. A layer of i foot depth
over the lake area of 88,000 square miles would contain 2,453
46 IRRIGATION.
billion cubic feet, sufficient to produce a discharge of 76,500
cubic feet a second for a year. In consequence of the great
regulating action of these lakes, with their enormous storage
capacity and evaporating surface, there is no such thing as
high and low water recognised on the river below. The wealth
of water carried by the St. Lawrence river pursues its way to
the Atlantic through the humid region where the rainfall is
copious — usually from 40 to 60 inches per annum, or even
more — so that it is not agriculture that benefits by the con-
stancy of the river discharge, but navigation only. For in the
eastern half of the United States it is drainage and not
irrigation that requires attention.
There are in Europe also natural reservoirs which act with
similar effect to the St. Lawrence lakes, but they are on a very
much smaller scale. The Po discharge has a constancy due to
the fact that li is drawn from Lakes Como, Maggiore and
Garda ; the Rhone is moderated by the influence of Lake
Geneva, and the Rhine by Lakes Constance and Neuchatel.
The aggregate area of the surfaces of these six lakes is less than
one hundredth part of the area of the St. Lawrence lakes above
the Niagara Falls.
The Yenisei river, in Siberia, is fed by the Baikal lake,
which has an area of 12,430 square miles.
The equatorial lakes of Africa are the most worthy rivals of
the St. Lawrence lakes in respect of the aggregate surface area
of the group, but their influence is divided between three rivers.
There is Lake Nyassa, of 9,000 square miles area, at the source
of the Shir^, a tributaryof the Zambesi ; there is Lake Tanganyika,
of 12,650 square miles, together with smaller lakes, at the source
of the Congo ; and the Victoria, Albert and Albert Edward
Nyanzas, of 29,000 square miles aggregate area, at the sources
of the White Nile. The Nile lakes certainly exercise a moderating
effect on the fluctuations of the White Nile, but, unfortunately
for Egypt and the Sudan, the moderating influence is carried
too far, as the lakes not only act as collecting and storage
SOURCES OF SUPPLY. 47
basins, but as evaporating tanks as well, with surfaces so
extensive in relation to their catchment areas that an excessive
proportion of the rainfall is lost by evaporation. And this loss
is increased to a serious extent in the enormous swamps known
as the Sudd region, which the water has to traverse on its way
to the North. Evaporation from the water surface of these
marshes and absorption by water plants reduces the discharge of
the river by more than a half.
However beneficial as moderators of extremes of high and low
discharges natural reservoirs may be, it is seldom that they act
conveniently in all respects without artificial control. In the
interests of navigation an extensive system of artificial reservoirs
has been constructed out of some of the many lakes at the sources
of the Mississippi river. Another fine example of such reservoirs
exists in Russia at the interlacing sources of the Volga and the
Msta rivers. By the water stored in these reservoirs, which
comprise several lakes, the navigability of the two rivers is main-
tained during the season of low water ; and, with the help of an
artificial waterway, the Volga is connected with the Msta, and
thereby the Caspian with the Baltic.
But instances of natural lakes under artificial control serving
rivers on which irrigation systems depend are rare. One such
instance there is on record, but the lake as an effective reservoir
is now extinct. Mention has already been made of Lake Mceris
as described by Herodotus. He was told by his guide that the
lake was an artificial one, and it seems that he believed it. But
he need not have done so, as the guide had no possible means of
knowing how the lake came into being, several thousand years
before he was born. There is little doubt that the crops of the
modern Fayum Province are grown on the bed of the ancient
lake. The lake would have had a surface area of about 700
square miles, and a superior layer of about 10 to 15 feet depth of
water which could have been used to supplement the river in
summer. It was not situated at the Nile sources, but some
3,000 miles below them, and about 60 miles above the apex of
48 IRRIGATION.
the Delta. Neither was it in the track of the river itself, for it lay
just outside the Nile valley, but was connected with the river by
a short branch, like a bud on its stalk. In this situation it was
most conveniently placed to act as a moderator of fluctuations
of level in the Deltaic branches of the river. This natural reser-
voir was brought under control by regulators constructed on
the channels of in-flow and out-flow, so that the flood water
could be admitted to the lake to the extent desiijed, and the
stored water be returned to the river when it was wanted.
Possibly this reservoir also was worked in the interests of
navigation only, but, as has been already suggested, it may have
also promoted the former prosperity of the northern margin ot
the Delta by providing a sufficient supply of water for cultiva-
tion at other seasons of the year than that of flood.
The Lake Mceris reservoir was in a peculiarly favourable
situation for moderating high floods and supplementing low
summer discharges in the Deltaic branches of the Nile.
Usually the lakes which act as natural reservoirs to rivers are
located near their sources, at a distance, sometimes very great,
from the point where any beneficial effect from their action
would first be felt. One great disadvantage resulting from the
distance is that much of the stored water is lost by evaporation
and absorption during its flow. Another drawback is the
difficulty of regulating the supply from the reservoir so as to
give the exact amount required at a distant point, where the
effect of any alteration of the reservoir out-flow would not be
felt for many days after.
In the absence of natural lakes, artificial reservoirs must be
made if storage of water is to be effected. \
The question of storage may either arise during the period of
design, or after a canal system has been some time in operation.
An artificial reservoir may be the essential feature of the
original irrigation project, and may be required to serve either
as the sole source of supply, or as supplementary to a river of
deficient discharge. But the necessity of a supplementary
SOURCES OP SUPPLY. 49
reservoir is not always recognised during the period of designing
an irrigation system. More often the necessity of supple-
menting the river discharges by storage does not make itself
felt until the effect of the irrigation, carried on with the
natural discharge of the river, has reached its full development
and the demand for water has increased in consequence of an
unforeseen expansion of the area brought under cultivation.
The recent history of irrigation in Egypt provides an
interesting example of the latter conditions. In 1884 the
newly appointed irrigation engineers from India commenced
the work of reform of the irrigation works in Egypt, which
they and their successors have carried on steadily ever since.
As the reform in means and methods took effect, the cultivation
became more intense and the area wider, until at length every
drop of the summer discharges of the Nile was utilised, and no
further*^ development of cultivation was possible without an
addition to the summer supply of the river. During the flood
and winter seasons, however, there is always enough water and
to spare in the river, so that there is a surplus available in those
seasons for storage. The further development of Egypt could,
therefore, be promoted by the creation of a reservoir capable ot
holding this surplus water in reserve for the summer months.
The study of projects for its storage was, therefore, undertaken.
The first calculation to be made, in the particular case
selected as an example, was one to determine the quantity
of water ^ that it was necessary to store in order to be
able to supplement the summer discharges of the Nile to such
an extent that Egypt might receive its full development. This
calculation made, it remained to decide to what extent the
first reservoir should provide for this, and also to ascertain
whether there was a sufficiency of surplus discharge to furnish
the quantity to be stored, without inconvenience to navigation
and other interests affected. To determine the quantity of
storage required, the first thing to do was to calculate the total
requirements of Egypt. Experience has shown that an
I. E
;0 IRRIGATION.
allowance of la cubic metres per day per acre of gross area
gives a gufficient supply for summer cultivation.'^ In round
figures the area of Egypt, including areas to be reclaimed and
exclusive of 500,000 acres to be permanently maintained as basin
land, may be taken as 7,000,000 acres. Consequently the total
daily discharge required in summer is 84,000,000 cubic metres.
The natural summer discharge of the river may be taken as
24,000,000 cubic metres a day. Therefore 60,000,000 cubic metres
a day is required from the reservoir for, say, one hundred days,
making a total quantity to be stored of 6,000,000,000 cubic metres.
No deduction is here made for evaporation in the reservoir, as the
summer discharge during the greater part of the hundred days
is considerably greater than 24,000,000 cubic metres a day, and
the quantity in excess of that discharge may be considered as
balancing the loss by evaporation.
It was necessary, also, to decide the best site for the first
reservoir to be made and its storage capacity. At the time that
these questions were being considered, the Mahdi was in power
on the Upper Nile, and the examination of reservoir sites was
restricted to the river below the second cataract. In con-
sequence of this limitation of the area of survey, Egypt has
probably benefited by getting its reservoir some years sooner
than it otherwise would have done. For, if the Upper Nile
had not been closed to him, Sir William Willcocks, who was in
charge of the reservoir study, would certainly have required more
time for the examination of other sites higher up the river, and
he would, doubtless, have come to the same conclusion in the
end. For there is probably nowhere on the Nile a more
favourable site for the construction of a dam than the crest of the
first cataract above Assuan, not only on account of the quality
of the rock and the disposition of the summer channels, but
also on account of the site being the nearest possible one that
^ Recent calculations are based on a larger allowance. See Notes 4 and 5,
Appendix IV.
SOURCES OF SUPPLY. Jl
could serve both Upper and Lower Egypt. If, then, Sir W.
Willcocks' studies showed that the storage capacity of a
reservoir which could be created by the construction of a dam
at Assuan was sufficiently ample, there was everything to
recommend the project, one thing only excepted, and that the
resulting submersion of the island of Philae. The basin of the
Assuan reservoir is the valley itself through which the Nile runs.
Bounded by high rocks, it is of little width ; consequently, to
have capacity, the reservoir had to be deep. Cross-sections of
the valley were taken to determine what the capacity of the
valley was with different water-levels, in order to furnish data
for a decision as to the height to which the Assuan dam should
be built. It was calculated that a dam holding up water to i6
metres above the natural low-water level would create a
reservoir capable of storing 1,065,000,000 cubic metres ; and that
if the dam were made 12 metres higher, the reservoir capacity
would be increased to 3,733,000,000 cubic metres. Eventually
it was proposed to build a dam to hold up to 24 metres above
low water, and thereby to create a reservoir with a storage
capacity of 2,550,000,000 cubic metres. But Egypt was not to
be allowed to go so fast. Strong protests from the archaeolo-
gical societies of Europe extracted a reluctant compromise
from the Government of Egypt, and the lower dam design,
which provided a storage of 1,065,000,000 cubic metres only,
was adopted. Europe has often interfered in the affairs of
Egypt, not always with advantage to the dwellers on the Nile,
and, in this case, with little satisfaction to itself At the time
of making this compromise it was calculated that the total
quantity of water required to be stored to supply the needs of
all Egypt and provide for its full development was 3,610,000,000
cubic metres, so that the Assuan reservoir, as decided on,
would hold less than a third of the total then supposed to be
required. Ten years later the figure for all Egypt was consi-
dered to be 6,000,000,000 cubic metres,^ of which the Assuan
' still later the figure was again increased. See Note 5, Appendix IV.
E 2
52 IRRIGATION.
reservoir, as limited by the compromise, provided 1,000,000,000.
leaving 5,000,000,000 still to be arranged for.
As the sources of supply for an irrigation scheme are being
considered, and Egypt furnishes a concrete example of a country
seeking means to still further increase its water supply, it may be
interesting to examine the suggestions which were made at that
time to obtain the increase. There were five possible ways of
doing it as then conceived : —
(i) The Assuan dam might be raised, and the capacity of its
reservoir doubled. (The raising of the Assuan dam was decided
upon in 1906 and the work was completed in 1912. Th« xtra
storage thus obtained is 1,200,000,000 cubic metres.)
(2) Another dam, similar to the Assuan dam, might be built
on the river at some suitable point higher up, to form another
reservoir in the Nile valley itself ;^
(3) A reservoir might be created in a depression known as
the Wadi Rayan, alongside the Fayum province, which would
be close to the site of Lake Moeris, and would act in much the
same way as the ancient reservoir, though it would be on a
smaller scale ;
(4) The loss by evaporation and absorption, where the river
spreads itself out through the Sudd region, might be
enormously reduced ;
(5) The lakes near the equator at the White Nile sources
might be controlled by regulation so as to serve as storage
reservoirs.
Enough has already been said about the Assuan reser\oir
and Lake Moeris to show in what way the first three alternative
projects would provide for feeding the river at low supply, and
on what data the calculations concerning their utility would
be based. The fourth method of increasing the supply, by
diminishing the loss due to evaporation and absorption, is an
unusual one, and the proposal is the outcome of the peculiar
conditions of the Upper Nile above Khartoum.
> A project for a barrage on the White Nile is approved ; but it is not
similar to the Assuan dam. See Note 6, Appendix IV.
SOURCES OF SUPPLY.
53
On the long line of river lying between the equatorial lakes
and Khartoum (see Fig. 6) the swamps, known as the Sudd
region, are traversed by the flowing water for a distance of
nearly 500 miles. In these swamps the river spreads itself
THE NlLEi
ABOVE
KHARTOUM
Fl G
KHARTOUM
1^
LAKE
Albert;
EDWARDi
on f Jt L L»
out over a vast area of unknown extent, escaping sideways from
the two more or less well-defined channels into which the river
divides itself where it enters the marsh tract. Over this expanse
of water-surface evaporation is active, while the papyrus and
other swamp-loving plants, stretching away in all directions
without visible limits, have a power of absorption proportional
54 IRRIGATION.
to the vast extent that they cover. Discharge observations have
shown that, of the water which enters at the upper end of the
swamps, 50 per cent, is lost in summer and 75 per cent, in a
high flood. The actual measurements give the following
results. During summer the discharge entering the swamps
at Lado is 600 to 700 cubic metres a second, of which only
300 finds its way out at the lower end of the Sudd region. In a
low flood the discharge entering is 1,000 cubic metres a second,
of which 400 reappears ; in a high flood 2,000 enters, and 500
comes out again.
If, then, this loss could be entirely prevented, the summer
discharge of the river could be increased from 300 cubic metres
a second to 600 at the point where it leaves the swamps. This
would represent an increase of 26,000,000 cubic metres a day
(over 10,000 cubic feet a second), which would go a long way
towards making good the present deficiency of the water supply
of Egypt ; for the increase would be equivalent to that which
would be obtained from a reservoir storage of 2,500,000,000
cubic metres. One great advantage in this method, over that
of storage in reservoirs, is that the river supply is not decreased
at any time of the year in order to obtain an increase at another,
but is increased at all seasons, a matter of some importance
when the quantity still required to supplement the river in
summer reaches such a high figure as 5,000,000,000 cubic
metres according to the then accepted estimate.
The method proposed, with the object of diminishing the
enormous loss of water in the Sudd region, is to form an
embanked channel from end to end of the swamps in order that
the river discharge may be prevented from spilling sideways
except at such times and places as may be found desirable. It
would not be economical or even advantageous to form a
channel large enough to carry the flood discharge ; therefore
some provision would have to be made for disposing of the
surplus water. The original suggestion was to construct
regulating works at the head of the proposed channel, so that
SOURCES OF SUPPLY. 55
only the required discharge should be allowed to flow into it,
and the surplus be escaped through masonry sluices to spread
about at will in the swamps and be evaporated and absorbed.
But a later, and probably better, proposal has been made for
the disposal of this surplus, and that is, to prevent it from
leaving the upper lakes at the river sources, and so to keep it
in reserve till it is wanted. The area of the lower and smaller
lake, the Albert Nyanza, is so great that a regulating work at
its outlet, designed to hold up not more than 3 metres (10 feet),
would probably give all the control necessary. The regulation
of the outflow of Lake Albert is another matter connected with
the storage question. At present the subject under considera-
tion is the method of adding to the available supply in the lower
reaches of the river by the avoidance of loss in the upper reaches.
In the example selected for illustration the means of prevention
consists in arrangements to lessen the waste by the confinement
of the discharge in a channel of uniform section adapted
to its volume. In the particular instance of the Nile swamps
the difficulty lies in selecting the most favourable alignment for
the channel, and in executing the work when the line has been
chosen. Either an existing channel must be enlarged and
embanked, or a new canal and banks be made along whatever
alignment may be found to be the most favourable. The
shortest distance possible would be that of a straight line
joining the river at Bor with the point where the Sobat river
ends in the White Nile, the length of which is 210 miles, as
shown in Fig. 6. The distance between the same points,
following the windings of the existing principal channel, is
440 miles, or more than double the distance along the straight
line. The length of channel to be formed must, therefore, be
something between 440 and 210 miles. This would in any
case be a formidable undertaking, but it is one which, if it
proved successful, would fully justify a very high expenditure.
But though the loss of water may be materially decreased, it
cannot be entirely prevented, as there must be some consider-
56 IRRIGATION.
able loss from evaporation and absorption in a canal of 300 miles
length, more or less, lying wholly within the tropics. Even if
there were none, and the discharge at the head reached the tail
in undiminished volume, the full requirements of Egypt would
still not be met, and additional storage somewhere would
be necessary.
If one or more of the three alternative projects of storage
already enumerated is not selected to supply the deficiency,
there still remains the fifth alternative of controlling the water
that leaves the equatorial lakes. That the lowest lake of the
three, the Albert Nyanza, has capacity enough to store all
that is wanted with a heading up of a few feet only, is easily
shown. The surface area of the lake is 4,500 square kilo-
metres. Before the Assuan dam was made Egypt was in need
of 6,000,000,000 cubic metres of stored water for use in summer.
The Assuan reservoir, now that the raising of the dam is com-
plete, supplies 2,300,000,000. The formation of an embanked
channel through the swamp region would effect an increase of
the summer discharge equivalent to that produced by a storage
of, say, 1,700,000,000 cubic metres. Consequently a further
storage of 2,000,000,000 cubic metres was required, according to
the accepted figures of those days. It is difficult to estimate
what proportion of such an increase would be lost on the long
journey (some 3,000 miles) from the lakes to Eg5^t, but it would
not be very great, as a moderate addition to an existing supply
would only slightly increase the evaporating and absorbing
areas. Hence, if 3,000,000,000 cubic metres of storage is
effected, it may be considered that sufficient allowance has been
made ior loss on the way, the allowance being 33 per cent.
The area of Lake Albert being 4,500 square kilometres, or
4,500,000,000 square metres, a layer of 70 centimetres (or
2 J feet) depth would represent a stored volume of 3,150,000,000
cubic metres ; and that is about what is wanted according to
the data assumed as to the total requirements.
It has now to be ascertained if the quantity of rain that
SOURCES OF SUPPLY. 57
reaches the lake from the gathering gronnd is sufficient to
provide for that storage. There are, in this particular case,
two ways of calculating what the quantity available for use is.
The one method is to calculate the quantity from what flows
into the lake from the gathering ground ; and the other, and
more accurate method, is to make the calculation from what
leaves the lake. As reliable data for making the calculation
by the former method do not exist, the second method alone
can be usefully applied to this case. The mean discharge of
the Alb« rt Nyanza outflow for the year, measured in the river
below the outlet of the lake, is ofiicially given as 769 cubic
metres a second. Assuming that the numerous torrents which
feed the river between the lake outlet and the head of the
proposed new channel give a sufficient discharge without any
help from the lakes for the four months of high supply, the
volume of the discharge of the Albert Lake outlet could be
entirely stored in the lake for these four months, and be added
to the normal discharge during the remaining eight months.
The quantity stored would be at the rate of 769 cubic metres a
second for four months, and the addition to the normal dis-
charge for the remaining eight months would, therefore, be
half that figure, or 384 cubic metres a second, equivalent to
33,000,000 cubic metres a day, or a storage of 3,300,000,000
cubic metres for use during the low supply period of one
hundred days. So it may be concluded that, if the data
are correct, the storage possibilities of the equatorial lakes
are not much more than sufficient to satisfy Egypt, even after
the Sudd channel has minimised the loss in transit through the
swamps.^
With the help of illustratia as borrowed from the Nile, the
following instances of water supply have been passed in review :
firstly, a supply derived from the natural discharge of a river
unaided by any reservoir; then, of a river with a lateral reservoir
to supplement its lower branches; again, of a river supple-
' See Note 4, Appendix IV.
58 IRRIGATION.
mented by a reservoir made in the valley of the river itself far
below its sources ; then again, of a river discharge being
increased by prevention of waste on the line of flow ; and
lastly, of a river fed by natural reservoirs brought under
control by engineering works of regulation. *■ There remains
one more class of reservoirs, of which the Nile furnishes no
example, but which is perhaps the most common in other
countries. This class includes artificial reservoirs made in
the upper part of the catchment of a river. Such a reservoir is
formed by the construction of a dam on the most convenient
site — usually across a gorge — whereby the discharges of the
higher tributary streams are intercepted and retained in the
valley which is converted into a reservoir by the dam.
The Indian Irrigation Commission (1901 — 1903) in its report,
among other recommendations for storage works in many parts
of India, proposes, in the interests of the Deccan districts of
Bombay, " that the catchment areas of all the rivers which
derive their supplies from the unfailing rainfall of the Western
Ghats should be carefully examined with a view to the con-
struction of as many large storage reservoirs as possible, and of
the works necessary for carrjnng the supply into those tracts in
which irrigation is most urgently needed."
Sir Thomas Higham, who was one of the members of the
Indian Irrigation Commission, stated in the discussion on Irri-
gation, St. Louis Exhibition Congress, 1904, that " almost all
future extensions of irrigation in India, with the exception of
the large canals that are still possible in Northern India and in
Sind, will involve the construction of storage works."
In the United States further progress in the irrigation of the
arid regions can only be brought about by the storage of flood
waters in reservoirs. For nearly the whole available flow of
the streams has already been appropriated by means of such
irrigation works as are within the power of individuals, corpora-
tions or societies to carry out. But the more formidable
engineering works that are necessary to effect storage are out-
SOURCES OF SUi-PLY. 59
side the possible limits of private enterprise, and fall within the
province of Government to execute. President Roosevelt in
his first message to Congress, 1901, admits this in the following
words: "Great storage works are necessary to equalise the
flow of streams and to save the flood waters. Their construc-
tion has been conclusively shown to be an undertaking too
vast for private effort. ... It is as right for the national
Government to make the streams and rivers of the arid region
useful by engineering works for water storage as to make use-
ful the rivers and harbours of the humid region by engineering
works of another kind."
The agricultural development of South Africa depends also
to a great extent upon the storage of water in reservoirs.
The essential feature of such storage works as those contem-
plated in India and the United States will be, in some cases,
a high dam designed after the type of dams already built for
similar purposes, of which examples will be given in the next
chapter.
Obviously the first condition that should be satisfied by any
storage project is that there shall be a sufficient volume of flow-
off the catchment above the dam to fill the reservoir to the height
necessary to provide adequate storage for the year's requirements
in any year of which the rainfall is not exceptionally bad. The
site of the reservoir must therefore be at a suitable distance below
the actual sources of the river system to which it belongs. If the
dam is to be a high one, it must have sound rock for its founda-
tion. Gorges, at the outlet of a mountain valley, from which
the hill-slopes above recede widely so as to enclose an expansive
area, are the most favourable sites for dams. The height of
the dam will be determined by the quantity that the reservoir
is to be made to hold and by the configuration of the basin
formed above it. A basin or valley with a gradually sloping
bed will require a less height of dam to effect the storage of
a given quantity than will be necessary if the slope of the bed
is more rapid. But a deep reservoir has this advantage over a
60 IRRIGATION.
shallow one, that a less proportion of water is lost by evapora-
tion.
It was remarked above that the scientific boundaries of
tracts of country, hydrographically considered, are the water-
sheds between their catchments. This scientific division has
been, in some cases, upset by irrigation engineers themselves
refusing to be bound by it. There are instances of the watef
supply of one catchment being diverted into a neighbouring
catchment by carrying it round or through the water-shed
ridge. This has been done on the Rocky Mountains in
Colorado. On the west side the supply exceeds the demand,
but on the east there is less than enough. Consequently the
supply of the west has been carried in channels or tunnels to
the east side of the water-shed, and made to do duty there.
"The Sky Line ditch," to cite a particular instance, carries
water in a channel cut in the rock round the mountain tops at
an altitude of 10,000 feet, and diverts it from one of the upper
tributaries of the Laramie river to Cache-la-Poudre valley,
Colorado.
There is a remarkable instance of the diversion of the water
of one catchment into another to be found in India. The
district of Madura, in Southern India, has frequently suffered
from famine, lying as it does on the eastern side of the Ghats,
where the rainfall is scanty and very uncertain. On the
western side of the Ghits, however, the rainfall, which is
copious and unfailing, under natural conditions finds its way
down the channel of the Periyar river and discharges itself
uselessly into the sea. At one point in its course the Periyar river
is separated by a few miles only from one of the tributaries of
the Vaigai, the river of the eastern catchment on which Madura
relies for its irrigation. At this point a channel of connection has
been made between the Periyar and Vaigai rivers, and, in addition,
a reservoir has been formed on the Periyar river for storing the
rainfall of its catchment. The Vaigai is thus fed by the rain which
falls on the other side of the water-shed separating it from the
SOURCES OF SUPPLY. 6l
Periyar catchment. The connection between the two consists of
a tunnel cut in the rock through the intervening hills, 5,704 feet
in length. • The reservoir of the Periyar river is formed by a
dam, 1,241 feet in length and 155 feet in height from river
bed to crest, built across a very narrow gorge. The reservoir
holds 13,300,000,000 cubic feet of water, of which the upper
6,815,000,000 only are available for irrigation. The catchment
above the dam has an area of about 300 square miles, and the
rainfall is said to be more than 120 inches in the year. The
reservoir has a water-sprea4 of about 12 square miles. But it
is not only the amount stored that is available for irrigation on
the Vaigai, but the discharge of the Periyar river as well ; so
that altogether a total volume of about 30,000,000,000 cubic
feet is diverted during the year from one catchment to the
other.
A bold project has been recently undertaken in India, which
also depends for its working on the use of the water of one
catchment for irrigation in another. A reservoir does not form
a feature in this project, as the rivers concerned are snow-fed.
The rivers are the Jhelum on the west, the Chenab in the
middle, and the Ravi on the east. There is land requiring
irrigation between the Jhelum and the Chenab, also between
the Chenab and the Ravi, and again on the east of the Ravi.
The Chenab and the Ravi have no water to spare, as existing
irrigation has claims to the whole supply. But there is water
to spare in the Jhelum. So it was decided to carry the surplus
of the Jhelum across to the Chenab, and thus release a corre-
sponding volume of the Chenab discharge for the irrigation of
the tracts to the east of it. This discharge is carried in a caneil
which irrigates the land alongside it between the Chenab and
Ravi rivers, and then passes the Ravi river by a level crossing
to irrigate the lands to the east of the Ravi.^
Further particulars concerning some of the more important
reservoirs and dams already constructed or projected will be
* See Note 7, Appendix IV.
62 IRRIGATION.
given in the next chapter. But before Keaving the subject of
supply, mention must be made of one of the earliest systems of
irrigation in India— the system of surface tanks. Thousands
of these tanks in Madras provide irrigation for millions of acres
of rice crops. They vary in size from a few acres to nine or ten
square miles of water surface. They are usually formed by
earthen embankments thrown across small local drainages,
often of only two or three square miles in area, or by a series
of such embankments thrown across the valleys leading from
larger catchments The Madras tanks depend mainly on local
rainfall, but are sometimes fed from rivers or streams by means
of channels taking off above weirs constructed in the beds of
the rivers.
The relative importance of the tank system in India, as
compared with other systems of supply, may be gathered from
the following figures :-^
Area in British India irrigated from wells . 13,000,000 acres.
„ „ „ „ canals . 17,000,000 „
„ „ „ „ tanks . 8,000,000 „
„ „ „ in various ways 6,000,000 „
Total area in British India irrigated . 44,000,000 ,,
Tanks are the primitive forms from which the more modern
and imposing reservoir has been evolved; but as the early
form is so well adapted to certain conditions, it has survived,
with but little modification, in those situations where the
conditions favourable to development to the higher type do
not exist.
In the United States there is a class of reservoirs which in
some respects resemble the Indian tanks. They are formed in
suitable places among the foothills or out on the plains where
convenient depressions exist in the neighbourhood of irrigable
farms. They are filled by large canals, taking off from a river,
with the surplus discharge which may not be needed for direct
irrigation, either during the flood or other seasons. From these
river-fed reservoirs the water is carried in canals to the fields to
be irrigated.
CHAPTER V.
DAMS AND RESERVOIRS.
The further agricultural development of India, Egypt, the
Western States of America, Western Canada, South Africa,
Spain and other arid countries depends largely on irrigation.
In the countries named, Canada only excepted, almost all future
extensions of irrigation will involve the construction of storage
works. The subject of reservoirs has, therefore, an increasing
importance to the present-day student of irrigation.
The climatic conditions which create a demand for and favour
the formation of storage reservoirs are a deficient or uncertain
rainfall during the period of the growth of crops, and at other
seasons a constant and heavy rainfall over the area from which
the crops obtain their water supply. Such are the conditions
which are usually associated with perennial irrigation, and it is
this which explains the almost universal need of storage works
in countries which have dry and rainy seasons. The more
valuable crops, as, for instance, sugar-cane and cotton, are
those which require watering during the spring or summer
months, when the natural water supply is often at its lowest.
Before looking for a reservoir site, it is necessary to ascertain,
from such rainfall statistics as may exist, whether a reservoir, if
made, will fill with sufficient regularity to justify confidence
being placed in it as a reliable insurance against deficiency of
supply. . If the rainfall statistics give encouragement enough,
the catchment area should be examined with a view to selecting
a favourable site for a reservoir. The nearer the reservoir is to
the land to be irrigated the better, for several reasons. Not
only will the loss of water in transit between reservoir and crop
64 IRRIGATION.
from evaporation and absorption be less, and the accommoda-
tion of the supply to the demand be easier, but the extent of the
collecting area will be greater than it would be if the reservoir
were removed to a site higher up the catchment basin. But,
as a rule, the configuration of the ground determines the best
site for the reservoir, and the selection of the site is not so much-
a matter of choice as a recognition of Nature's decision in the
matter.
When the situation of the future reservoir is known, the
question of its annual replenishment can be studied. The
period and amount of rainfall, the proportion of flow-off to
total rainfall, and the area of the catchment, are the necessary
data rec^uired for the determination of the question. The
catchment area can generally be measured with sufficient
accuracy on existing maps; otherwise a survey will have to
be undertaken to ascertain the lie of the watershed lines and
the area enclosed by them. The rainfall statistics are generally
imperfect, and the p.oportion of flow-off a most difficult thing
to estimate. ( That the rainfall statistics are usually imperfect
is not surprising, considering what is held to constitute com-
pleteness of the rainfall record. It is not enough to have the
rainfall readings of one or two stations in the catchment.
The observations must be made in at least as many sites in the
catchment as will give values representative of all the local
variations in the annual amount of the rainfall. Moreover, to
include all the cyclical changes, the statistics should embrace
the observations of thirty-five years, as less than this may not
include years of extreme conditions. If, however, the records
do not exist, there is no choice but to make the best of imperfect
data, and to allow a wide margin of safety.
But, even though the rainfall statistics may be as complete
as could be desired and the catchment area accurately known,
there will still remain much uncertainty as to the quantity that
will reach the impounding basin. Only a proportion of the
rain that falls on the catchment area flows off it. The rest
DAMS AND RESERVOIRS. 65
is evaporated or absorbed. The amount that is evaporated
varies with the temperature and the hygrometric condition of
the air. The amount absorbed varies with the nature of the
soil and its degree of dryness or saturation at the time of rain-
fall, and depends on the surface slope and configuration of the
collecting basin, and on the presence or absence of trees or
smaller vegetable growth. The proportion of flow-off is also
affected by the intensity of the rainfall. In Chapter IV. of
Buckley's " The Irrigation Works of India," and in Strange's
"Indian Storage Reservoirs," valuable statistics of "flow-off"
from different catchments in India are collected, and the con-
clusions to be drawn from them discussed. It appears that
the conditions of rainfall and catchment may vary to such an
extent that the proportion of flow-off to total rainfall may
correspondingly vary from nothing to 98 per cent. It would
seem, then, almost a waste of labour to attempt to calculate
the quantity of water that will reach the reservoir with factors
of which one is so variable as the figure representing the pro-
portion of flow-off. And so perhaps it would be in the absence
of a somewhat intimate knowledge of the nature of the catch-
ment area and of its rainfall, or without the experience necessary
to make correct deductions from such knowledge. Consequently
it is better, whenever it is possible, to base the estimate of the
quantity of flow-off on the discharges of the streams which
actually drain the area, if, by any means, they can be even
approximately determined.
Still, the subject of calculating quantities of flow-off by
means of rainfall and catchment figures cannot be dismissed
by throwing discredit on the data commonly available, as there
may be no other method possible of arriving at any conclusion
concerning the prospects of filling the reservoir and as to the
allowance of escape waterway that must be provided to pass
off any excess reaching the reservoir when it is full. The flow-
off and its relation to the rainfall have been carefully studied
in the case of many reservoirs in India, and, in the hands of
1. r
66
IRRIGATION.
anyone competent to make proper use of it, the record of the
observations made forms a useful guide for estimating the
flow-oif from catchments which are known to have similar
characteristics to any of those to which the record applies.
Perhaps the conditions which most affect the proportion of
the flow-off are the state of the catchment at the time of rainfall
and the intensity of the rainfall. Mr. Strange gives the follow-
ing figures as a rough approximation of what may be expected
from an ordinary drainage area : —
Rainfall in
Inches in
Twenty-four
Condition of the Catchment,
Percentage of Flow-ofTto Rainfall.
Dry.
Damp.
Wet.
0-25
0-50
I -00
2"00
3-00
4-00
and over.
Nil.
NU.
5
10
20
30 to 40
Nil.
10
14
35
40
50 to 60
12
14
20
34
55
70 to 80
In India it has been found that, in tracts where the rainfall
in the five monsoon months is about 40 inches, the percentage
of flow-off has an average monthly variation represented
approximately by the following figures: —
Assum
Bd Rainfall.
Flow ofi.
June
6 inches — 5 per cent, of rainfall
July . .
II
.. —15
If )>
August .
II
.. —35
» »
September .
8
■• —50
» II
October
4
» —30
» I*
With a monsoon rainfall of less than 40 inches the percentage
of flow-off would be less. These figures, however, must only
be taken as relatively correct, and as indicating in a rough way
the manner in which the percentage of flow-off varies with the
saturation of the soil and the intensity of the rainfall.
DAMS AND RESERVOIRS. 67
The result of the calculations of flow-off will serve to show
(if the data used have been correct) whether the catchment
will furnish the quantity of water required to make the reservoir
a success as a main or supplementary source of supply to an
irrigation system., To be a success, the supply must not fail
in years of deficient rainfall ; though some hold that it is not
necessary to insist that it must be equal to the demand in years
of exceptionally scanty rainfall, which come but seldom.
Whether shortcomings in such years may be deliberately con-
templated as admissible in the preparation of a reservoir
project, must depend on the circumstances of the particular
case. But a reservoir which fills in years of ordinary rainfall
when its assistance may not be much wanted, and fails to fill
in years of deficient rainfall when there is urgent need of its
help, does not justify its existence and the cost of its
construction.
Assuming, however, that the study of the rainfall and catch-
ment conditions have led to the conclusion that the replenish-
ment of the reservoir is assured, there remains another matter
to investigate. It is most important to determine the maximum
discharge that the by-wash or escape of the reservoir will have
to pass. An under-estimate of what this may be might be
followed by disastrous results. The fate of the Nadrai
aqueduct in India conveys an impressive lesson. This
aqueduct carried the Lower Ganges Canal over the Kali Nadi,
a channel which drains an area of 2,377 square miles. The
waterway allowed under the aqueduct for the discharge of the
Kali Nadi was calculated on the basis of the then highest
recorded flood of 23,000 cubic feet a second, equivalent to
9 cubic feet a second per square mile of drained area, or
0*33 inches in depth over the entire catchment in twenty-four
hours. In July, 1885, a flood of 130,000 cubic feet a second —
six times as great as the maximum previously recorded — caused
a rise at the aqueduct of 20 feet above the highest water mark
of previous years, and destroyed the work. The aqueduct has
F 2
68 ' IRRIGATION.
since been rebuilt and a sufficient waterway provided for the
safe passage of 140,000 cubic feet a second, which is, since the
accident, the accepted figure for the maximum discharge of the
Kali Nadi.
To guard against such an unwelcome surprise as was
experienced in the case of the Nadrai aqueduct, it is necessary
to ascertain the maximum discharge from the catchment in
periods of heaviest rainfall and greatest flow-off. So it is
desirable to have a record, not only of the daily rainfall, but
also of the heaviest rainfall that occurs in shorter periods than
a day, even sometimes in fractions of an hour. Unfortunately
it is not likely that this information will be obtainable, at any
rate during the period of study of any new reservoir project.
So, again, it will be better, if possible, to calculate with what-
ever figures may be obtainable from observations on the
streams by which the flow-off reaches the reservoir. There
may be a record of discharges kept; or, if there is no such
record, discharges may be taken expressly for the purpose of
the reservoir study. The residents of the locality may, possibly,
be able to point out the highest marks reached at different
places along the course of the streams by the greatest flood
known to them. From these marks the surface slope of the
flood can be ascertained, and with the gradient thus determined,
and with cross-sections of the waterway taken opposite the
marks, the flood discharges can be calculated. This method
of estimating the maximum discharge which flows off a catch-
ment will give more reliable results than calculations based on
rainfall statistics and an assumed value for the proportion of
flow-off. But if the former method is not practicable, the
latter must be followed faute cU mieux. In the calculation of
the maximum flow-off, the time occupied, or the rate of flow,
is an important factor. In steep and barren catchments the
rate is rapid, and the total flow-off arrives in the reservoir in a
shorter time than it does from catchments of gentle slope or
wooded surface. Also from small catchments the flow-off is
DAMS AND RESERVOIRS. 69
rapid relatively to that of large catchments. As the circum-
stances of every case differ so widely, it is impossible to lay
down rules for calculating what discharging capacity should
be given to the reservoir escape. The peculiar circumstances
of each case must be studied and the allowance determined to
the best of one's judgment. Formulas there are which are
used in India to work out what discharge per square mile of
drainage area the reservoir escape should provide for, but the
correctness of the results obtained depends altogether on the
discretion with which the formula is used. The co-efficient,
which is the controlling factor of the formula, varies from 150
to 1,000, and even more. The use of any of the formulas does
not avoid the necessity of a right judgment of the special
conditions affecting the particular case under consideration.
With this warning the formulas most commonly used are given
below. In both of them
D = discharge in cubic feet per second,
M = area of catchment in square miles,
C is a co-efficient.
(i) Dickens' formula : D = C 4/ M*
(2) Ryves' formula : D = C v^"M*
In Madras, Ryves' formula is generally used with the following
values for C :-~
Within 15 miles of the coast — 450,
Between 15 and 100 miles from the coast — 563.
For limited areas near the hills — 675.
In the Bombay Presidency the waste weirs of tanks and
reservoirs are designed to discharge from 212 to 967 cubic feet
per second per square mile of catchment, the allowance varying
with the amount of average annual rainfall, with the area of
the catchment, and with the slope of the river above the reser-
voir. In other parts of India the discharge which the reservoir
escape is designed to pass may vary between 150 and 600 cubic
feet a second per square mile of hill areas, and between 25 and
160 from areas in the plains. But there is a case of a tank in
70 IRRIGATION.
India, fed by a rocky catchment of small area, in which the
discharging capacity of the waste weir is as much as 1,936 cubic
feet per square mile; and another as much as 3,514 cubic feet.
The latter, if not also the former, is probably in excess of
requirements. '
The storage capacity of the reservoir may be limited by the
physical features of the site, the amount of flow-off from the
catchment that can be relied upon, or by the requirements of
the land to be irrigated. As a rule the demand is greater than
the maximum supply possible, and it is the volume of the flow-
off that determines what capacity should be given to the reservoir.
There are limits to the height to which it is safe or practicable
to build dams to store water, and the configuration of the ground
maybe such that no reservoir site can be found which will contain
the required volume of storage without constructing a dam of a
height exceeding the maximum permissible. The capacity of
the Assuan reservoir in Egypt was limited for exceptional
reasons. The temples on the island of Philse had worshippers
whose vigorous protests against the submersion of buildings
which some of them had never seen, resulted in the dam being
built at first to a height 26 feet lower than was originally
intended. The capacity of the reservoir was thus reduced from
2,500,000,000 cubic metres to 1,000,000,000.*
The gross capacity of a reservoir is calculated from the areas
bounded by the contours between the high water level of the
reservoir and the reservoir bed. Its " available capacity," or
the quantity that is supplied by the reservoir through its outlet,
is the volume stored between the high water level and the sill
of the outlet, less the loss due to evaporation and absorption in
the reservoir after it has been filled and replenishment ceases.
The deduction to be made on account of evaporation depends
upon the length of time the water is stored after the final
replenishment, and on the temperature and hygrometric state
* The subsequent raising of the dam by 23 feet has increased the capacity
to 2,200,000,000 cubic metres.
DAMS AND RESERVOIRS. 7 1
of the air for that period. Observation alone can determine
exactly what the deduction should be. There is also a loss
from leakage and absorption depending on the nature of the
bed of the reservoir. It may be taken roughly as equal, in the
year, to half that due to evaporation. The loss due to evapora-
tion in a year, measured in vertical height, may vary from
3 to 10 feet, according to the climatic conditions.
The dam, which is the principal feature of a reservoir project,
may be made of earth or of masonry, or of a combination of
both. There are dams of a type peculiar to America known
as " rock-fill " and " loose rock " dams. They are formed of a
mass of rubble with a water-tight facing, which may be of
planks, of asphalt or Portland cement concrete, of masonry,
of steel plates, or of earth. Another type pecuUar to America
is a dam, either of earth or loose stone, with a central core of
steel plates forming a water-tight diaphragm embedded in the
mass of the dam.
Masonry dams may be classified as —
(a) Solid submergible dams, over the crest of which the
discharge passes ;
(6) Solid insubmergible dams, with waste weirs to discharge
excess water, and outlets for the delivery of the stored water;
(c) Insubmergible dams, pierced with numerous sluices,
through which the discharge is passed.
Earthen dams must always be insubmergible, and be pro-
vided with waste weirs and outlets. They may be divided into
three classes, namely, —
(i) Dams with masonry core walls ;
(ff) Dams with central puddle core ;
(/) Dams entirely of earth without core walls.
The question as to which class of dam is the most suitable
for any particular site depends to a great extent on the nature
of the foundation. ^ A high masonry dam must have sound rock
for its foundation. This is a sine qua non. An earthen dam
may be built on sandy or gravelly clay, fine sand or loam, and
72 IRRIGATION.
also on rock if proper precautions are taken to prevent creep of
water between the bed "of the dam and the rock surface.
Earthen dams can be safely built up to 75 feet in height,
though French engineers fix the safety limit at 60 ifeet. No
doubt 60 feet is a safer limit than any greater height, but there
are earthen dams in India, exceeding 75 feet in height, which
have now been tested by many years of useful work. There
are in existence also earthen dams of 80 and 100 feet in height,
and one of even 125 feet. Mr. Strange considers that embank-
ments above 75 feet in height should be reinforced by adding
dry stone toes to the slopes, and that, with this addition, dams
might be safely constructed up to 125 feet in height. He
admits, however, that when a height of 60 feet is exceeded
particular care must be taken both with the design and with
the construction.
The choice between earth and masonry for the dam construc-
tion is affected also by economical considerations, and the
f actilities for transporting materials to the site of the work.
As earthen dams are doubtless of earlier origin than masonry
dams, they will be considered first.
The design and construction of earthen dams has been treated
fully by Mr. W. L. Strange in his practical treatise on " Indian
Storage Reservoirs with Earthen Dams " (1913), from which
much of what follows relating to them is borrowed.
The design of an earthen, dam includes the dam proper, the
waste weir, and the delivery outlet. The safest arrangement is
when each of these three works are separate one from the other,
the waste weir being on one side of the dam and the outlet on
the opposite side. But for the sake of economy, or other
reasons, they 'are often combined in one work. The more
common arrangement is to combine the dam and outlet in one
work, and to separate the waste weir. If the three works are
separate, and there is no outlet passing through the dam, it is
probably best to construct the dam entirely of earth of the
same character throughout, the soil selected being of a descrip-
DAMS AND RESERVOIRS. 73
tion that is impervious and stable under the action of water.
The cross section of such a dam of ordinary good soil, if from
50 to 75 feet in height, should have the following dimensions: —
The crest of the dam should be 6 or 7 feet above the high
water level of the reservoir; the crest width should be 10, feet ;
the up-stream slope on the reservoir side should' have 3 of
base to i of rise, and the down-stream slope 2 to i. If
the dam is 15 feet high or under, the crest of the dam may
be 4 to 5 feet above high water level, the top width 6 feet,
up-stream slope 2 to i, and down-stream ij to i. For dams of
heights between 15 feet and 50 feet the dimensions may be
intermediate between the foregoing.
It will be necessary to protect the up-stream slope between low-
water level and high-water level with a skin of dry rubble revet-
ment, or of some other suitable material, to resist the erosive
action of the waves of the reservoir; and the down-stream
slope also must be so clothed as not to be guttered by rainfall.
The reinforcement of the slopes of earthen dams of more
than 75 feet height by the addition of dry stone toes is desirable
to give security against sliding. The down-stream stone toe is
also useful in providing for the drainage of the heart of the
dam without injury to the down-stream face, and is, on this
account, preferable to the solid masonry retaining wall which
has been added to some dams as a support to the down-stream
slope. The Maladevi Tank dam ^ in Bombay was designed as
an earthen dam with dry stone toes. At its highest point it is
subjected to a water pressure of 98 feet. Its up-stream and
down-stream slopes are 3 to i and 2 to i respectively, but
these. slopes change above high-water level. The up-stream
face above high-water level is protected by a crest wall of
masonry vnth a batter of | to i, the down-stream slope changing
to 1 1 to I. The up-stream wall of masonry protects the crest
from wave-wash, acting as a breaker. It also prevents burrowing
animals from injuring the dam.
• The Maladevi Tank dam was not built, another site having been preferred.
74 IRRIGATION.
In the construction of earthen dams, particular attention
must be given to the foundations. Not only must precautions
be taken to prevent creep of vs^ater between the natureJ ground
and the artificial earthwork of the dam, but provision must be
made for intercepting any percolation water that may travel
through the subsoil^ or for leading it harmlessly away. Also,
to prevent the dam itself becoming saturated and consequently
slipping or subsiding, it is necessary either to guard against the
water entering the dam, or to provide means of getting rid of it
if it does enter. Thorough drainage of the earthwork and of its
foundations is, therefore, the condition essential to security. To
the endeavour to exclude the water from the dam, cut off the creep
at or below foundation level, and provide drainage for the dam and
its foundations, the different types of earthen dams are due.
The first condition for the adoption of an earthen dam in a
storage project is that the soil of the foundations and that for
the construction of the dam itself must be suitable, the one to
withstand the weight of the dam, and the other to resist the
passage of water and any tendency to saturation.
Borings into the foundation, or trial pits, will reveal the
nature of the subsoil and furnish the information necessary for
determining the measures to adopt in each case. If the sub-
soil is porous (and most subsoils are more or less), or if it is of
rock with porous seams, the usual course is to make a puddle
trench under the centre of the dam to offer a water-tight
obstacle to the movement of the water, so that all down stream
of it may be kept dry. The bottom width of this curtain should
not be less than 6 feet for small dams, nor less than lo feet
for high dams. The usual rule is to make the base width equal
to one-quarter of the full supply depth of the reservoir at any
given point. The depth of the puddle trench will depend upon the
porosity of the soil and the head of water in the reservoir, and
may vary from half the depth to the whole depth of the full
supply storage in the reservoir, or more. The trench must
be carried down until it enters for a feet at least into good
DAMS AND RESERVOIRS. 75
clayey soil extending downwards. Or, if rock is met with
before reaching these depths, the trench should be carried at
least I foot down into the rock to form a good joint with it,
Tf sandy and highly porous layers exist to a great depth, it may
be necessary to condemn the site and give up the project.
To cut off the creep between the natural ground and the
artificial bank above it, the puddle filling of the trench should
be continued upwards past the plane of junction for a foot or
more, so as to make a bond with the earthwork of the dam.
The foundation of the dam should also be benched to present
surfaces for the dam to rest on slightly inclined /towards the
centre of the dam. Along the bottom angles of this benching
which are up stream of the main puddle trench, small puddle
trenches should be formed parallel to the main trench, and along
the angles of the down-stream benching trenches should be
made and filled with porous material to serve as foundation
drains. In the design of the Maladevi Tank dam, where it rests
upon rock, concrete walls, sunk in the rock surface, take the
place of the puddle curtain barrier.
But, if the material of the dam is not absolutely water-tight,
water will find its way through the mass of the dam to the
down -stream face, possibly to a dangerous extent. To provide
against this, the puddle trench has been sometimes developed
into the puddle core by carrying up the puddle as a thin wall,
in continuation of the puddle in the foundation trench, from
the bottom of the dam to above high water level. By this
means the penetration of water into the mass of the dam is
confined to the half of it up stream of the puddle wall, and the
stability of the down-stream half is not affected by any soakage.
Regarding the dimensions to be given to puddle walls opinions
differ, but Rankine's rule is that the thickness at the base should
be about one-third of the height, and the thickness at the top
two-thirds or one-half that of the base.
The objection to a puddle core is that it is liable to rupture
from unequal settlement of the earthwork of the dam, and it
76
IRRIGATION.
then ceases to be water-tight. For this reason, masonry core
walls are to be preferred, though, generally speaking, their cost
would be considerably greater. But a masonry core wall
requires solid and sound rock for its foundatioh, and therefore
cannot take the place of a puddle core unless this condition is
fulfilled. If the waste weir or outlet, or both, are combined
with the dam in one work, the masonry core wall adds con-
siderably to the security, as it enables a perfectly sound bond
CROTON DAM
EARTHEN LENGTH
FIG 7
^£vnn-.QP,..*526--=^-
Scale
of iiiimiiil
25.4 be^ow xero
too 290 „ .
I T 1 1 Feft
to be made between the dam and its associated works. This
is important, as an outlet, for instance, passing through an
earth dam without a masonry core wall, is always a source of
weakness, offering a line for leakage if there should have been
anything defective either in design or execution.
Whether the core be of puddle or masonry, it must be con-
tinued outwards to both flanks up to high water level, the changes
of level in the foundation bed of the core at the flanks being
effected by vertical rises. Great care must be taken to form a
good bond between the dam and its natural abutments lest a
leak should form between the two. Opinions differ also as to
the dimensions that should be given to masonry cores. The
earthen length of the New Croton dam. New York, is con-
sidered to be of good design (Fig. 7^). It has a masonry core
'■ The earthen length after partial construction was altered to a solid
masonry dam.
DAMS AND RESERVOIRS.
n
which is carried down to a depth of 125 feet below the original
surface ; for 89 feet from its foundation level it has a width of
18 feet, and thence it gradually decreases to a top width of
6 feet at a level 14 feet below the crest. This dam has a
height of 120 feet above the original ground surface. It abuts
on to another length of dam in masonry.
The position of the water-tight component of a dam in the
centre of the embankment is theoretically an unfavourable one.
The water enters the up-stream half of the dam and reaches the
O
FOY SAGAR TANK DAM
PIG 8
core wall. It is thus the impermeable core wall, backed up
by the down-stream half of the dam, which does all the retaining
work. The up-stream half is only useful in preventing the wall
from falling inwards towards the reservoir when the latter is
empty. So dams of a section, such as that of the Foy-Sagar
Tank (Fig. 8), would appear to answer all the purposes of a
full-section earth dam, provided the wall is strong enough to
hold up its backing when the reservoir is empty, r The dimen-
sions of the face wall of the Foy-Sagar Tank dam are certainly
remarkably light, and are even less than those of the core wall
of the Kair Tank dam (Fig. 9) which has a support of earth
on both sides.
78
IRRIGATION.
In consequence of the theoretical objection to the situation
of the impermeable diaphragm in the centre of the mass, a
puddle surface has sometimes been given to the reservoir face
of the dam to prevent the water from entering the bank at all.
But there is a practical drawback to this arrangement which
has caused its rejection : the puddle is liable to slide and crack
when the water level in the reservoir is low or the embankment
settles, and so to be no longer water-tight. The puddle core
in the centre of the dam, on the other hand, is protected, by
reason of its position, from the effects of the weather, and has
no tendency to slide or crack, so that it is more likely to remain
KAIR TANK DAM
ScaU
ip 6 IB y
FIG 9
«0 M
^^ F>et
Bl
'WEJR.CIIUT.I,
EARTH
water-tight. But with a masonry core wall this argument does
not apply, and the up-stream half of the dam, as has been
stated, only serves to support the wall when the reservoir is
empty. As a masonry core wall cannot be built except on
rock foundations such as would be suitable for a masonry dam,
it would be a matter for consideration whether, instead of an
earth dam with a masonry core or face, it would not be better
to substitute a masonry dam.
There seems to be a growing tendency to prefer one of the
two extremes, either an earthen embankment of uniform section
and homogeneous material without any core wall, or a dam
wholly of masonry. Between these two extremes lie all the
composite varieties of dams. It is possible that one or other
of the varieties may be found more suited to the special
DAMS AND RESERVOIRS. 79
conditions of a particular site than the aH-earth or all-masonry
dam would be.
Dams of the American type form a class by themselves. The
dam with a central water-tight diaphragm of steel plates, how-
ever, belongs to the class of dams with masonry or puddle
cores, as its principle of action is the same. It differs only as
regards the material of which the dam is made in those cases
in which dry rubble is substituted for earth to form the mass of
the dam on either side of the core. The steel plate is embedded
in a concrete base forming a junction with the bed-rock. In
such a dam the principle is recognised that the core alone stops
the passage of water, and the material on either side of it
merely acts as a support to enable it to resist the pressure.
Instances of this class of dam are to be found in Southern
California.
" Loose-rock " dams are simply dams made of dry rubble
with an impervious up-stream face of tarred planking or earth.
The safe section for this class of dam is not much less than
that of an earthen dam : the upper and lower slopes, however,
can be made steeper than those of an earthen dam ; but 2 to
I for the upper slope and i to i for the lower is as steep
as they should be made. A facing of earth, supported by loose
rubble below water, is not a good disposition of material.
Wood also, being perishable, is not a good material for use
in a permanent structure. So this type of dam is not in favour,
nor is it likely to be.
The " rock-fill " dam is made ot a mass of loose rubble
with a front and back wall of masonry forming steep sloping
faces. On the upper face there is sometimes added a covering
of two thicknesses of planking with tarred paper between, the
joints of the outer planks being caulked and the whole face
painted. The "Walnut Grove" dam, built in this way, had
a greatest height of no feet. It was topped and destroyed by
a flood in 1890, the waste weir proving insufficient for its
purpose. The dam of the Castlewood reservoir in Colorado,
8o
IRRIGATION.
another of this type, still exists as the only specimen of its
class. Its section is given in Fig. lo. This kind of dam may
be classed with the composite masonry and earth dams of the
Foy-Sagar variety (Fig. 8), dry rubble taking the place of the
earth backing and acting as a support to the face wall in the
same way.
Such dams as " loose-stone " and " rock-fill " are of an
inferior class to the all-masonry dam. The masonry dam,
founded on sound rock, has fewer weak points in its constitu-
tion than other forms, and for certain situations is the only
CASTL&WOOD RESERVOIR DAM
W.L. /'» Seserv oir
■■>.
form that could stand. Nothing but a masonry dam, for
instance, would have been possible for the Assuan dam on
the Nile. Examples of the three classes of masonry dams —
the submergible, the solid insubmergible, and the pierced in-
submergible — are given in Figs, ii to 22, 25, and 26. A
selection has been made from among dams of recent con-
struction, as embodying the ideas of modern engineering
concerning the design of high masonry dams, so far as recent
work affords examples. The main dimensions of these dams
are shown on the iigures, and they will therefore, as a rule,
not be given in the text.
The variety in design of existing dams is great, but in the
DAMS AND RESERVOIRS. 81
high dams constructed during recent years there is a tendency
to uniformity of design where the conditions are similar. This
is no doubt the result of a general acceptance of the theory of
stresses in dams, which mathematical investigators had, till
quite lately, held to be sound. The soundness of the theory,
on which the design of most modern dams has been based, has
now been called in question and is being put to the test.
The forces acting on a dam are — (i) the pressure of the
water in the reservoir exerted in a direction at right angles to
the up-stream face and (2) the weight of the dam itself acting
vertically.
In a masonry dam the conditions of stability, as commonly
accepted, are three, namely, —
(i) The lines of pressure, both when the reservoir is full and
when it is empty, must lie within the centre third of the cross-
section ;
(2) The pressures in the masonry or on the foundations
must never exceed safe limits ;
(3) The friction between the dam and its foundation bed, or
between any two parts into which the dam may be divided,
must be sufficient to prevent sliding.
Compliance with the first condition gives security against
overturning. Until lately it was assumed that it also precluded
the possibility of tensile stresses on the masonry. But the
justification for this assumption is now questioned, and it is
contended that, if the dam is treated as an elastic solid, it is
necessary to take account of the elastic shear as well as the
elastic compression. Mr. Atcherley holds that- it is not suffi-
cient to consider the stresses in horizontal sections, but the
stresses in vertical sections also must be investigated, and it
will then be found that tensions exist in the toe of the dam to an
extent that cannot be disregarded. Sir Benjamin Baker,^ after
discussion of this question, and admitting that tension in
masonry should be avoided as far as possible, expressed
" Vol. CLXII. " Proceedings Inst. C.E.," pp. lao, 456.
I- * G '
82
IRRIGATION.
his opinion that, " whatever theory mathematicians might
evolve, engineers would not be relieved from the obligation
to use no materials for dams which would not stand, say,
fifty tons per square foot in compression and ten tons per
square foot in tension without splintering." In existing dams
the actual maximum pressures vary as a rule from six to
fourteen tons per square foot.
In practice it is found that if the above conditions (i) and (2)
are satisfied, so also is condition (3).
Masonry dams of great height were first built in Spain.
H.W.L.
10 ao Ao 40
I I H Feet
W.L. DO WW stream/
The Alicante dam, of 140 feet greatest height, was built
between the years 1579 and 1594; but the Almanza dam,
68 feet high, was built at some unknown date long before.
Nearly all the dams of Spain are built across mountain gorges
on rock foundations.
The construction of the Furens dam in France, between the
years 1862 and 1866, marks the next great advance in dam-
building. The French engineers were the first to work out
the scientific principles according to which dams should be
designed, and to test their soundness by applying them to
actual practice. The Furens dam, of a greatest height of
DAMS A.ND RESERVOIRS.
83
177 feet from foundation to crest, was the first dam to which
these principles were appHed. Its section is given in Fig. 17.
It belongs to the insubmergible class.
Submergible dams, of which examples are given in Figs. 11
to 16, exhibit heavier profiles relatively to the height of the
dam than those which are insubmergible. The submergible
dams act as overflow weirs, and have to support the extra
LA GRANGE DAM
pressure due to the depth of water which flows over their crests,
and also to resist the action of falling water on the down-stream
side. Many, if not most, of the dams that belong to this class
have subsidiary weirs associated with them. These weirs are
built in the channel some distance down stream of the main dam
with the object of holding up the water above them to form a
pond or water-cushion on which the falling water may expend
its force. The toe of the dam and the rock adjacent is thus
G2
84
IRRIGATION.
protected from scouring action. The Betwa dam, in India,
(Fig. ii) has a solid platform of masonry for its down-stream
toe, the upper surface of which is submerged lo feet by the
water ponded up by a subsidiary weir i8 feet in height. The
shock of the falling water, moderated by the water-cushion, is
thus borne by the solid projecting platform.
VYRNWY DAM.
ft
5LL? 'P
' iHl l ll l I
SeaHi
it
±iJ
fee*
I
!
t
I
FIQ 13
■
The Turlock, or La Grange dam, in California, (Fig. 12)
has similarly a subsidiary weir, 20 feet high, situated 200
feet from the main dam. But it has no platform down
stream, and its cross-section differs greatly from that of
the Betwa Dam. The Turlock profile is, however, the
more common form of the two, and is typical of a large
number of existing submergjble dams. The Turlock dam
DAMS AND RESERVOIRS.
85
is designed for a maximum depth of i6 feet of water flowing
over its crest.
The cross-section of the Vyrnwy dam, in Wales, (Fig. 13)
CROTON DAM
MAXIMUM SEOTION OF
SUBMERGIBUE LENGTH
Scale
TTENARES WEIR
'i ' ' I ' y '■' ' '? I-
Scale .
10 IB.
90'
— t-
^
^ feei
FIQ 16
exhibits, though in not a very pronounced form, the ogee
down-stream face. There is a cushion of 45 feet depth of water
over its toe. The force of the falling water is, moreover,
broken up during its descent over the down-stream face by the
86
IRRIGATION.
roughness of the surface. Very large stones were available for
the building of this darn, and were used in the down-stream face
with the roughest possible exposed surfaces. In consequence
of this arrangement the overflow, according to the description
given by Dr. Deacon, reaches the pool below as " white spray ",
instead of as " solid water,"^ the force of its fall being expended
on the rough projecting surfaces of the down-stream face stones.
This is as it should be. It is a mistake, sometimes made, to adopt
the ogee curve for the down-stream face and to make the surface
smooth. With such an arrangement the water glides evenly
VIR NALA DAM
Scale
FIG 16
30
■^
3 Feet
H.W.t.
over the crest and down the slope of the dam with a delusively
harmless appearance. But the less resistance the water meets
with during its descent, the greater will be its velocity and its
power to work mischief on its arrival at the toe. The mistake
was made in India on the Ganges canal when it was first
constructed. "» The weirs were originally given ogee profiles, but
they have since been converted into stepped weirs, or weirs with
vertical drops, so as to prevent excessive horizontal velocity.
The Henares weir, in Spain, has the ogee form (Fig. 15). It
should be classed, perhaps, as a river regulator rather than a
» Proceedings Inst.C.E., Vol. CLXIL, p. no.
DAMS AND RESERVOIRS. 8/
submergible dam ; or it may be considered an intermediate type
between the Indian anient and a dam of the Turlock form. It
is founded on rock which has sufficient strength to resist the
action of the high velocity current acquired by the water in its
unimpeded passage from above to below the weir.
The canal head-works at Vir Wadi on the Nira river in
India include a dam which is a combination of two weirs,
FURENS DAM
10 10 m ipo
Sca/e of Id Iii i i I I I I I T I I I -M Feel
made up of a main weir across both the Nira river and the Vir
Nala and a subsidiary weir down-stream on either channel.
Both weirs are founded on rock. The subsidiary weir on the
Nira river is over i.ooo feet distant from the main weir, but
that across the Vir Nala (Fig. i6) is only about 40 feet distant.
The objection to such an arrangement as that shown in Fig. 16
is that boulders may get imprisoned between two weirs so near
together and, under the action of currents and eddies, may work
88
IRRIGATION.
deep pot-holes in the rock bed at the toe of the main weir.
This combination of weirs should be classed with the Henares
weir as intermediate between a river-regulating weir and a
submerged dam. It acts as both.
The highest submergible dam in existence is that of Mun-
daring, in Australia, It has a greatest height of 190 feet from
PERIYAR DAM
Scale
Feet
W.LS
foundation to crest, which latter is 100 feet above the original
surface of the ground. It is designed for a depth of overflow
of 5 feet. In August, 1904, there was an overflow of 18 inches,
the actual maximum up to that date.
Of the examples of solid insubmergible dams given in Figs. 17
to 22, the Furens dam has already been referred to.
The Periyardam, in India, (Fig. 18) forms the most important
DAMS AND RESERVOIRS.
89
feature of the irrigation scheme to which reference was made
in the preceding chapter as furnishing an illustration of the
diversion of the water of one catchment for use in another.
The dam is built in a narrow rocky gorge 269 feet wide at the
bed and 1,241 feet wide at the parapet level of the dam. The
reservoir came into operation in 1896.
MARIKANAVe DAM
10 10
lllllUlll I
Scale.
68. 100
I I i I f I * I I Fett
FIG 19
HW.L. fc n j
The Marikanave dam, in India, (Fig. 19) is also built in a
gorge, which is 1,200 feet broad at the dam crest level. The
reservoir formed by it is the largest in India, and has a gross
capacity exceeding that of any other reservoir in the world,
excepting only the Assuan reservoir on the Nile. Its water-
spread is 34 square miles, and maximum capacity 30,000,000,000
cubic feet. The storage capacity of the reservoir is, however,
90
IRRIGATION
greatly in excess of the calculated annual jeplenishment, so that
it is not expected to fill more than once in six years. It was
for economical reasons that the dam wais given the extra height
which has provided the excess storage. ^Sir Thomas Higham
has explained how such a proceeding could result in economy.
" The average annual rainfall is not more than 25 inches.
CROTON DAM
INSUBMERGIBLE LENGTH
W5-D0
and the inflow due to such a fall will probably not exceed
10,000,000,000 cubic feet. In some years it may be less, or
even nil. It was originally proposed to provide a capacity of
20,000,000,000 cubic feet, which would about equal the inflow
due to an annual rainfall of 30 inches ; but there were records
of cyclonic rainfalls, the run-off of which would not only fill a
' " Irrigation,'' Transactions American S.C.E., 1904.
DAMS AND RESERVOIRS. 91
tank of this capacity, but would also require an overflow capacity
of 60,000 cubic feet a second. Such an escapage could only be
provided by cutting a deep channel of adequate dimensions
through hard rock, and, as a matter of arithmetic, it was found
to be cheaper to increase the height of the dam, and to place
the bed of the escape at a higher level."
The New Croton dam, which was substituted for the proposed
Quaker Bridge dam, has been constructed to impound water for
the supply of the city of New York. Like the Titicus dam, it
is made up of three sections which furnish illustrations of the
earth dam with masonry core (Fig. 7), of the submergible
masonry dam (Fig. 14), which serves as the waste weir or
overfall to the reservoir, and of the solid insubmergible masonry
dam (Fig. 20). The insubmergible length has a height of
300 feet at the point where the foundations are lowest, a
height which would have been considered extreme not many
years ago.^
The above-mentioned insubmergible masonry dams, chosen
as typical examples, are all either built on straight alignments
or on a curvilinear trace so flat as to be considered straight in
calculating the dimensions of the dam. The Furens dam, for
instance, has a curvature of 827 feet radius, but its profile was,
nevertheless, designed as if for a straight dam. There are a
few dams, closing narrow gorges, which depend for their
stability on the fact that they are built to a curved plan which
brings into play the principles of the arch. The outer ends of
these dams abut on the rocky flanks of the gorge, to which the
water pressure is transmitted. The transverse dimensions of
the dam can, therefore, be reduced considerably, and it is no
longer a necessary condition of stability that the line of pressure
when the reservoir is full, must lie within the centre third of the
cross-section. But the weight of the dam itself must, neverthe-
less, be borne by the foundations, so that the condition that the
pressure in the masonry or on the foundations must never
* As with the Assuan dam, the foundations of the New Croton dam
had to be carried down a considerable depth — over 40 feet— below the
foundation level shown on the design.
92
IRRIGATION.
exceed safe limits, must still be complied with. The following
statement gives details about four remarkable curved dams,
three of which are in California : —
Name of Dam.
Country.
Maxi- .
mum
Height.
Radius
of Cur-
vature.
Length
of Dam
at Crest.
Top
Width.
Bottom
Width.
Feet.
Feet.
Feet.
Feet.
Feet.
Zola. .
Sweetwater .
Bear Valley
Upper Otay
France .
California
11
133
go
64
75
158
323
300
359
205
380
450
350
19
12
3-2
4
43
46
20
14
See Fig. 21
See Fig. 22
Figures 21 and 22 give the cross-sections of the Zola and
Bear Valley dams.
Reservoirs that are formed by solid dams holding up water
to considerable heights are doomed to extinction by silt deposit,
sooner or later according as the proportion of silt, that is carried
in suspension by the streams that fill them, is great or small.
The small scouring sluices, with which some of such dams are
provided, are efficient in removing the deposit of silt only in cases
where the reservoir is very narrow and has a very steep sloping
bed. India, Algeria and Spain can furnish instances of reservoirs
that have become extinct by the silting up of their basins. In
Spain, the Val de Infierno dam,^ 115 feet high, has been for
many years a useless waterfall, the reservoir basin having silted
up to the crest of the dam. The reservoir above the dam of
Alicaute, in Spain also, silts up to a depth of 40 to 50 feet
against the dam in four years. The scouring sluice is then
brought into operation, and the deposit removed by the escaping
water. At least, this should be done every fourth year ; but the
intervals between two scouring operations is generally longer.
In the case of the Alicante dam, the sluice acts well and the
reservoir is kept clean, probably because the basin is narrow
and steep. As the scouring sluice qf the Alicante dam is
typical of the sluices of both Spanish and Algerian dams, Sir
' " Irrigation du Midi de I'Espagne," by Aymard.
DAMS AND RESERVOIRS.
93
William Willcocks' description of such a sluice will be given.
Figs. 23 and 24 are referred to in the following description :
" The under-sluice at Khamis (in Algeria) is on the Spanish
principle. It is situated at the bottom in the line of the bed of
the original stream. A Spanish under-sluice consists of an
opening of from i to 3 metres in height, and from i to 2 metres
ZOLA DAM BEAR VALLEY DAM
Scale
PIQ 22
in width at the up-stream end ; it increases gradually as it
advances down-stream, and it is sometimes as much as 4 metres
wide and 6 metres high. , This opening is closed at the up-stream
end by a wooden door, called a Spanish door, supported against
horizontal timbers let into apertures in the two sides at the
point A in the figures. Just above the under-sluice is a
gallery. This gallery is about a metre wide and 2 metres
high, and is closed on the up-stream side, and open on the
94
IRRIGATION.
down-stream face to allow workmen to enter. It communi-
cates with the under-sluice by an opening some 60 centimetres
in diameter just down-stream of the gate A (Fig. 23).
The door is put in position in the under-sluice from the down-
stream side when the reservoir is empty, and the three horizontal
timbers B, C, D (Fig. 24) are let into slots in the jambs, and
the whole door is well caulked. The water now rises in the
reservoir, and as the deposits accumulate, they bury the door
and gradually gain great consistency. It takes four years for
SPANISH UNDERSLUICES
FOR. SCOURING
FIQ 23
FJG Z+
////////////////// 4
y/////y/^///A
the deposit to become solid, though it is generally left ten years.
When the reservoir has got filled up with deposits to the extent
which is considered a maximum, the workmen enter the under-
sluice, bore with an auger through the door to be sure that the
mud is solid, saw the timbers B, C and D, and then escape into
the gallery. The door is now free to drop, but it is generally
held by the solidified mud. The workmen now go to the top
of the dam and work a hole through the deposit with a long
iron pole until the water touches the door. When this happens
the door falls, and the mud follows it in a tremendous avalanche.
The reservoir is soon emptied, and more or less of the deposit
DAMS AND RESERVOIRS. 93
removed. A new gate is then put in, new horizontals B, C, D
are placed behind it, and the reservoir begins to fill again."*
Recognition of the liability to obliteration by deposit of silt,
to which most reservoirs formed by solid dams are subject, led
to the design of an insubmergible dam pierced with numerous
BHATGARH DAM
SECTION ;
THROUGH UNDER SLUICES
Scal^ of lill l l l l li T I [ zfc
40 50
I I Feet
Rock
ms<^M^4:<z^
SLUICE
-\
Id ■
>
< y////////////^ ^/; {^////^////y/'y.
)CK
under-sluices. The first specimen of this class of dam was the
Bhatgarh dam in India (Fig. 25), constructed about 1892.
This dam has a maximum height of 127 feet. There are two
overflow waste weirs, one at each end of the dam. But there
are also 15 under-sluices, each 8 feet by 4 feet, piercing the
dam near its centre, with their sills 12 feet only above the bed
I " Perennial Irrigation, etc.," Government of Egypt (1894).
9^ • IRRIGATION.
of the river, which is 103 feet below the crest of the dam. The
object of these sluices is to prevent the deposit of silt in the reser-
voir by providing a passage for the early Hoods at a low level.
If the flood water, heavily laden with silt, were to be discharged
over the high level waste weirs, it would drop the greater pro-
portion of its silt on the bed of the reservoir in its passage
through the deep pond above the dam. In ordinary floods
the discharge through the under-sluices is effected under a head
averaging 15 feet, and the ponding up extends to a distance of
3 miles above the dam. Consequently a certain proportion
of silt will be deposited in the reservoir, even when the under-
sluices are open to pass the early floods. But as they are
closed on July 31st, or earlier, to ensure the filling of the
reservoir, there will be a further deposit due to the later floods
which enter the reservoir basin after the low level exit is closed.
Still it is a great point gained that, at the time when the floods
are carrying the greatest amount of silt, the discharge is
allowed to flow forward through the reservoir with a com-
paratively small heading-up. The surface of the backwater,
when the under-sluices are open and working under a head of 15
feet, is less than one thirtieth of the area of the reservoir when
full ; and, therefore, twenty-nine thirtieths of the reservoir bed
are out of the reach of silt deposit. On the remaining thirtieth
under water there is also less tendency to deposit than there
would be if the discharge from the reservoir had to find its
way over the high level waste weirs. Undoubtedly the action
of the under-sluices will be effectual in prolonging the life of
the reservoir : the experience of the last twenty-five years
has demonstrated this.
The principle of allowing the silt-laden waters of floods to
pass through the reservoir basin without serious diminution of
velocity has been applied in a more thorough-going way to the
design of the Assuan dam on the Nile. This dam (Fig. 26) is
remarkable as being the first insubmergible dam built without
any provision of overflow waste weirs to discharge excess water.
<
o
DAMS AND RESERVOIRS.
97
The whole river discharge at all times of the year is passed
through sluices pierced in the body of the dam, as may be seen
on Plate I., which is a reproduction from a photograph taken by
the author on the day after the inauguration of the dam. The
Jam is also remarkable on other accounts. It is about ij miles
ASSUAN DAM
SaUe
lUIMIIIII
±
=1=
40
Feet
long, and, as originally built, even before the subsequent raising
and strengthening, contained over a million tons weight of
masonry. Moreover, the available capacity of the reservoir,
formed by it in the trough of the Nile itself, is greater than
that of any artificial basin in the world. The gross capacity
of the Marikanave reservoir in India is said to be 30,000,000,000
cubic feet, but this can scarcely be reckoned as available
I. H
98 IRRIGATION.
capacity, since the reservoir is only expected to fill once in
six years. A reservoir in Australia on the Upper Goulboum
river has been credited with a capacity of 60,000,000,000
cubic feet. The Assuan reservoir, with the dam as originally
built, was said to contain 1,065,000,000 cubic metres — or
37,611,000,000 cubic feet. After the raising of the dam by
5 metres (16-4 feet) and of the surface level of the reservoir by
7 metres (23 feet) above the level used in the calculation which
gave a resulting capacity of 1,065,000,000 cubic metres, the
new capacity has become 2,200,000,000 cubic metres — or, in
round numbers, 80,000,000,000 cubic feet. The greatest height
of the completed dam is 143 feet. It has now to support a
maximum head of 90 feet. The cross section of the dam, as
built in the first instance, and with the additions to it subse-
quently made, is as shown in Fig. 26.
The past history of reservoirs is sufficiently full of warnings
of the danger that would be run if a solid dam were constructed
to impound such a river as the Nile. During the flood months
of August and September, and sometimes October, the Nile
water is heavily charged with matter in suspension. Any
obstruction such as a solid dam, which materially interfered
with the flow during those months, would inevitably induce a
heavy deposit of silt, and eventually cause the obliteration ot
the reservoir basin. The dam might survive, but merely as a
picturesque waterfall like the Spanish dam of Val de Infierno.
To avoid this danger, the Assuan dam was designed to pass
the whole Nile flood through under-sluices. Of these there are
180 in number, all of them 2 metres (6J feet) wide, the 40
upper sluices being 3*5 metres (11 J feet) high, and the 140
under-sluices 7 metres (23 feet) high. They are placed in
groups at four diff'erent levels in the dam, a convenient arrange-
ment for regulation. An extreme flood of 14,000 cubic
metres (494^500 cubic feet) a second, which comes but
seldona, would be passed through the under-sluices, all being
open, with a heading up of about 3-5 metres (11^ feet)
DAMS AND RESERVOIRS. 99
and with a resulting velocity of about 6J metres (21 J feet)
per second. An ordinary flood will be passed with a heading
up of 2 or 3 metres (7 to 10 feet) only. Thus the turbid
flood discharge will be scarcely interfered with, and there will be
no danger of serious silting. Under normal conditions of the
river discharge the sluices remain open till the end of October,
when the water becomes comparatively clear. During November,
December and January the reservoir is filled by the gradual
closure of the sluices, commencing first with the lowest groups.
During February and March the reservoir is kept full ; and in
April, May and June its stored water is drawn upon to supple-
ment the deficient discharge of the river. Before the end of
July all the stored water has been discharged, and all the
sluices are open ready to pass the rising flood.
The Assuan dam had been in action for two years when
the question of raising it came up for decision. During
that time the severe action of the water, discharging through
the sluices with a high velocity, had eroded the sound
granite beyond the down-stream toe of the dam. To have
raised the dam and to have thereby added to the head
of water would have increased the severity of the erosive
action of the sluice discharge. As extensive protective
works, estimated to cost about a quarter of a million pounds
and to take two years to complete, were necessary to secure the
dam, as it stood, against danger from erosion of its natural
granite talus, the decision as to the raising was postponed till
this work should be complete. The granite bed of the river
below the sluices had been originally left in its natural rough
state with an irregular suriace, as may be seen in the
accompanying photograph : it was found necessary to substi-
tute an apron of masonry in cement mortar with a smooth
surface to protect the rock from the shock of the falling water
and to support the toe of the dam, The protective aprons
having successfully stood the test of two whole seasons, it was
thereupon decided to raise the dam.
u 2
100 IRRIGATION.
The postponement of the consideration of the question of
raising the Assuan dam had another advantage. It gave
time for the further investigations of Professor Pearson's and
Mr. Atcherley's new theory concerning stresses in dams,
which will be found stated shortly in an abstract of Mr. L. W.
Atcherley's Paper, published in Vol. 162 of the Proceedings
Inst.C.E., November, 1905.
In the Assuan dam there is no waste weir or outlet sluice ;
the under-sluices take their places. In the Bhatgarh dam the
under-sluices do only a small part of the work of passing the
reservoir discharge, and are in action for a short period only
during the year ; the waste weirs of the crest, on either flank
of the insubmergible portion of the dam, provide for the
outflow from the reservoir for the rest of the year. Sub-
mergible dams have no separate waste weirs, being themselves
waste weirs. But insubmergible solid dams and earthen dams
must have their waste weirs, and care must be taken that the
discharging capacity of these weirs be ample. The neglect to
provide sufficient waterway for surplus water to escape has
caused the ruin of not a few dams. If the waste weir is high,
it often takes the form of a submergible dam, as in the case of
the overfall portion of the Croton dam (Fig. 14). Some weirs
have no crest shutters, discharging capacity being obtained by
length of crest with shallow depth of overflow. But sometimes
it is more convenient, from want of space or for economical
or other reasons, to increase the depth of overflow rather than
the length of weir. In the waste weirs of the^Bhatgarh dam
many of the vents are fitted with the automatic gates invented
by Mr. Reinold. Fig. 27 shows the principle upon which these
gates work. Each gate is suspended by chains connecting it
with a counter-weight which is free to move up and down in a
water-tight chamber formed in the thickness of the weir wall,
An inlet pipe admits water to the cistern when the reservoir is
at full supply level, and an outlet pipe at the bottom allows it to
DAMS AND RESERVOIRS.
lot
escape. The discharge of the outlet pipe at its maximum is
less than the maximum discharge of the inlet pipe. It will be
observed from the drawing that the sluice is closed when the
gate is raised. The automatic action is produced by water
finding its way to the cistern and reducing the lifting power of
REINOLDS AUTOMATIC
SLUICE GATE
Scale 0/ ? I I I M I I I I y I I I 1 T Fiet
FIQ 27
Gale oteu i^K'
the counter-weight through immersion. When the water in the
reservoir rises to the level of the inlet pipe, the cistern gradually
fills and the counter-weight is immersed. When the counter-
weight has in consequence lost sufficient weight, the gate becomes
the heavier and moves downwards below the level of the sluice
sill, and continues to do so as long as the water rises in the
102
IRRIGATION.
cistern. When the discharge through the opened sluice lowers
the water in the reservoir below inlet level, the cistern empties
itself of water by its outlet pipe, and the counter-weight regains
the weight necessary to pull up the gate and close the sluice.
Before leaving the subject of dams, it may be useful to give
the figures representing the actual maximum pressures on the
masonry in some existing dams, selected from among old and
recent ones.
Name of Dam.
Maximum Pressure.
Tons per Square
Foot.
Weight of Masonry.
Pounds per Cubic Foot.
Almanza, Spain .
Alicante, Spain .
Verdon, France .
Gros Bois, France
Bhatgarh, India .
Assuan, Egypt .
Marikanave, India
Mundaring, Australia
Quaker Bridge, New '
^ork
1283
1034
5-80
14-60
7-27
5-80
•8-0O
•800
i6-6o
(designed)
160
143-5
150
(New Croton dam
substituted)
• Pressure not to be exceeded in accordance with conditions laid
down for de^gn.
Wilson's "Manual of Irrigation Engineering" gives the
following values for the limiting pressures which are ordinarily
accepted as safe to allow : —
Brick
770 tons per square feot.
Sandstone
■ 835 „ „
Limestone
, 9-80
Granite
. lOOO , „
From six to eight tons per square foot may be taken as the
pressure generally considered permissible in important dams of
recent construction. Bold things, however, are done in
America, and the New Croton dam may show that engineering
DAMS AND RESERVOIRS. IO3
practice in the design of dams has erred on the side of caution.
It will be observed that the pressure allowed for the Marikanave
dam in India and for the Mundaring dam in Australia is half
that allowed in the design of the New Croton dam, New
York.
CHAPTER VI.
MEANS OF DRAWING ON THE SUPPLY.
The supply of water, as already pointed out, may be drawn
from wells, rivers, natural or artificial reservoirs, or tanks.
When a storage reservoir forms a feature of an irrigation
system, the supply drawn from it may either be carried to the
distributing channels from which the lands are irrigated in a
canal or canals taking off direct from the reservoir itself, or be
sent on its way along the natural channel of the river to the
point where the canal system takes off. It is only from the
smaller class of reservoirs, which are called tanks in India, that
the distributaries are fed direct. The low-lying reservoirs of
the United States, which are filled during the flood season by
canals taking off from a river, may be classified as " tanks " ;
they deliver their water direct to the channels that distribute it
to the fields.
When wells are the source of supply, various mechanical
means are used to raise the water. For small lifts the shadouf
of Egypt — the Idt or picottah of India — is commonly used ; for
deep wells in India the mote is substituted ; for medium lifts
the Egyptian sakia or Persian wheel is universal. The shadouf
and sakia are also used extensively, along river margins for the
irrigation of small holdings. The province of Ddngola, at one
time reputed to be the richest province in the Sudan (a reputa-
tion of no very high order), is irrigated almost entirely by sakias
along the river edge, assisted by a very few only on wells.^ This
province will therefore furnish reliable statistics of what a sakia
is capable of doing, and it is worth while to note the figures. In
1904 there were at work in Dongola 3,892 sakias, 3 pumps
^ There has been a certain development of flood season irrigatioit of the
basin type of late years.
J
MEANS OF DRAWING ON THE SUPPLY. 105
driven by engines of an aggregate of 50 horse-power, and
51 shadoufs. The 50 horse-power pumping plant and 51 shadoufs
may be assumed to be equivalent to 58 sakias, bringing the total
number oi sakias up to 3,950. The area of taxed land in 1904
was 58,057 acres. The population was 130,000 souls, inclusive
of merchants, tradesmen, mechanics, etc. So that there was
I sakia to every 15 acres of taxed area, and 2*24 persons per
acre or 33 per sakia. Apparently the area under cultivation
had reached the limit that the population was capable of taking
in hand, as there was at least three times that area of cultivable
land available in the province, of which two-thirds was lying
fallow.
The area of crop that each of the contrivances named can
keep watered is small, and naturally varies with the lift. A
single shadouf is only equal to the irrigation of one or two acres
of crop ; a mote orsakia can irrigate, on the average, eight acres.
Shadoufs are often worked in tiers, one above the other, so as
to effect a total lift of 15 feet or more. The Persian wheel and
the mote can be readily adapted to varying heights of lift by
altering the length of the endless chain carrying the water
buckets or pots in the one case, and of the rope and bullock run
in the other.
These primitive watering contrivances of the East are well
adapted to farms of quite small areas, and to communities
wanting in mechanical skill and possessed of no appliances for
the handling of more elaborate machinery.
It is an idea that suggests itself to most who give their minds
to irrigation problems that the energy of the wind could with
advantage be utilised to raise water. But the wind is a more
capricious servant for irrigation to rely upon than rainfall. In
Holland windmills for lifting water are becoming obsolete : the
reliability of pumping stations worked by steam power has
discredited the qualifications of the wind. But in the arid
west of the United States wind power is not despised, as its
cost is about two-thirds of that of steam power. A windmill in
I06 IRRIGATION.
America can be depended upon for the irrigation of about
three acres ; but if a tank, to act as a reservoir to store water
at times when irrigation is not being carried on, is associated
with the windmill and its pump, from five to fifteen acres can
be given irrigation. This contrivance also is, therefore, only
suited to small holdings, and to irrigation on a very modest scale.
In the Fayum Province in Egypt and on the Genii river in
Southern Spain undershot wheels, carrying pots or buckets at
their circumference, are made use of to lift water on to high
lands alongside. An ordinary lift for such wheels is 15 feet.
The amount of water lifted for each revolution of the wheel is
small, but the delivery into the high level trough is continuous.
To work the wheel a drop of from 2 to 3 feet is required.
Plate II. gives a view of one of these wheels in Egypt, and
Plate III. of a similar wheel in Spain.
For large estates and irrigation on an extensive scale some
more efficient means of drawing oa the supply must be
employed. In Egypt the introduction of cotton and sugarcane
cultivation brought so much gain to the farmer that he was
able to afford a centrifugal pump, worked by steam power, for
the irrigation of his crops. Sir William Willcocks, in " Egyp.
tian Irrigation " {1913), gives the number of such pumps as
nearly 7,000. Twenty-one years ago the Eg5^tian Government
itself was on the point of adopting powerful pumping stations
as the sole means of drawing its water supply from the river,
and had actually made a commencement of putting that policy
into practice, when better counsels prevailed. For, when
irrigation is on the scale of the Government system of Egypt,
there is a more effective and economical way of getting the
river water into the canals than by pumping it. The method
consists in raising the low water level of the river by wholly or
partially damming its summer channel, so that the required
discharge may be forced to flow into the canal or canals taking
off from above the dam. By this means the difference of level
between the land and water surfaces at the canal head is
WATER-LIFTING UNDERSHOT WHEEL, SPAIN.
MEANS OF DRAWING ON THE SUPPLY. 107
diminished. The canal, connecting the pool above the river
dam and the land to be irrigated, is given a water surface slope
of a less gradient than that of the land surface, so that, after a
certain distance from the canal head, land and water surface
come to one and the same level.
The means employed for heading up the summer level of the
river at the canal offtake will first be considered. Different
countries seem to have their own peculiar type of work by
which this heading up is effected. The Indian type is the
"anicut," a submergible solid weir, over which the flood flows,
the control of the levels and currents being provided for by
what are known as under-sluicesj or scouring sluices, on one or
both flanks of the weir, and sometimes also in the centre. The
Egyptian type is the " barrage," of French origin, as its name
betrays. A barrage may be described as an insubmergible
river regulator, formed of piers resting on a platform at river
bed level and rising above flood level. Vertical grooves are
built into or cut in the piers, and shutters slide up and down in
them. By lifting or lowering the shutters the level of the water
in the pool above the barrage is controllfed. In flood-time all
the shutters are lifted above the water level, and the river flows
unchecked through the vents. For general convenience, arches
are turned between the piers, and a roadway is thus provided
between the two banks of the river.
In France there are several types of river regulators of
ingenious, and sometimes elaborate, designs. The early Poiree
dams were of the needle kind with iron trestles as supports to
take the pressure of the water when the needles were in place.
The Boule shutters later on were substituted for the needles,
the Poiree frames being retained. The BouM shutters are
merely sluice gates, lying one above the other in tiers vertically
and side by side in rows horizontally, fitted each one with a
bent iron strap whereby to get hold of and raise it. Another
form of closure is the Camere curtain,^ which consists of narrow
• " The Improvement of Rivers,'' by Thomas and Watt.
I08 IRRIGATION.
horizontal strips of wood hinged together and capable of being
rolled up by a chain which passes round them, each curtain
reaching from the surface of the water to the sill, which is near
river bed level. 'The curtains are supported by frames, which
either lie flat on the floor during flood, or are lifted up clear of
the water by overhead machines, so that the river passes freely
without obstruction of any kind. These systems, however,
suffer from the usual delicacy that attends complication of
structure, and, moreover, are ill adapted to rivers in which there
is floating debris. To obtain a tight closure when any debris
has clung to the frames is an impossibility with the Camere
curtains and a difficulty with the Boule shutters.
The " Chamoine " system, of French orig;in, has been
imported into America, and good examples of this form of
regulation are to be found on the Ohio and on other rivers in
the States. The " Chamoine" apparatus consists essentially of
three parts, viz., the shutter itself, the pivoted frame on which
the shutter rides, and the strut. The sill is formed of a narrow
ridge on the floor. The bottom of the shutter, when erect,
bears against the up-stream edge of the sill. The frame, or
" horse," upon which the shutter rides, moves about its pivots
on the floor immediately down stream of the sill. The shutter
is hinged near its middle to the outer end of the " horse " about
which it revolves, and is free to assume any position between a
horizontal and a vertical one. The strut supports the shutter
and its " horse " when they are raised and in the closed
position. The lower end of the strut rests against a casting on
the floor. When this is moved from the strut end, the shutter
falls under the pressure of the water, turning about its hinge
along the upper end of the " horse " until it lies flat behind the
sill with " horse " and strut beneath it.
In America irrigation on a large scale is of comparatively
recent growth. Practical experience with old and new ideas in
the design of irrigation works, and the lessons of experience in a
country quick to learn, will doubtless, in due time, result in the
DAM 0\ THE RIVER GENIL. SPAIN.
MEANS OF DRAWING ON THE SUPPLY. IO9
evolution of a form of river regulator which will be recognised
as the American type. " Rock-fill " and " crib " weirs can only be
considered as works of a temporary nature, destined to be
replaced by more permanent structures when and where the
interests affected are important enough to justify and to bear
the increased cost of construction.
Perhaps the best known irrigation system in Spain is that
which serves the fertile plain of Granada, stretching away from
the foot of the hill on which the Alhambra stands. Here,
round about the last foothold of the Moors in Spain, are to be
found swift-flowing canals meandering along the steep hill-
sides and through intercepting rocks down to the green plains
beyond the town of Granada. The water is derived from the
river Genii and its tributary the Darro, which joins it at
Granada. The head works of the canal system are primitive
in the extreme, and are probably as they were in the time of
the Moors. Plate IV. shows the regulating dam across the river
Genii below the head of the principal canal. It is constructed
of weighted trestles of the form shown in Plate V., which is the
photograph of a spur made at a spot a short distance above the
site of the dam. But the dam, though primitive and in need
of restoration after every severe flood, is efficient, if it is to be
judged by the results that are visible from the Alhambra
gardens.
The selection of a site for the river work which is to hold up
the water will depend upon many things. The work must
naturally be at such a point on the river that the canal which
takes off from above it shall deliver its water at country surface
at the upper limit of the land to be irrigated " free-flow," that
is, by gravitation or simple flow without the necessity of any
lift. The distance from the first point of irrigation should, for
the sake of economy, be as short as possible consistently with
the fulfilment of the condition concerning the delivery of water
at country surface. But it is not always possible to secure the
minimum. The material of the river bed, its cross section the
no IRRIGATION.
■ f ■
direction of the channel above and below, the nature of the
river banks, and much else, will have to be taken into considera-
tion in the selection of the best site. In the case, hbwever, of
a river work intended to head up water for the canals of a
deltaic system, the selection of a site is restricted to compara-
tively narrow limits, as the work must of necessity be placed at
the head of the delta where the river throws off or divides into
branches.
The height to which the summer level in the river is to be
headed up must, be first decided. The greater the heading up,
the shorter will be the length of canal along which the water
must flow to come to ground level. The usual head for a river
regulator is from lo feet to 13 feet. In Chapter 1 1., a figure (No. 5
was given showing the principle of grading a canal fed by a
river in flood, so that, after the necessary length of flow, the
water should spread itself over the land. In flood the natural
levels of the river, under the conditions assumed in the figure,
are only a few feet below country level, so that, after a
comparatively short run, the water in the canal comes to
country level. But in summer the levels of the river are so
Iqw that, if a canal takes off from it at its natural level, it will
have to flow a long distance before its water comes to land
surface. So it is better to raise the river level artificially, and
reduce this unprofitable length of canal. Supposing, for
example, that the country level is 10 units above summer water
level, and that it has a slope in the direction that the canal
will take of i in 10,000 units. If, in such a case, the canal is
designed to flow with a water surface of i in 20,000, then the
summer water will come to the land surface after a run of
200,000 units, or — adopting, for convenience' sake, metres as
the unit — 200 kilometres (Fig. 28). Now, supposing that
the summer level of the river is artificially raised 4 units, or
metres, the canal water comes to land surface at a point
120,000 units, or 120 kilometres, from the head instead of 200
kilometres. This arrangement results in a great saving of
RIVER SPUR, SPAIN.
MEANS OF DRAWING ON THE SUPPLY. Ill
expenditure on the earthwork of the canal excavation, balanced
to some extent by the cost of the head works in the river.
But, neglecting the question of economy, this advantage has
been gained, namely, that the country between kilometres 120
and 200, or on a length of 80 kilometres, is now commanded
by the canal and can be given free-flow irrigation. The diagram
(Fig. 28) shows the country level and the summer water levels
as they would be with and without artificial heading up of the
river.
It has been stated above that 10 feet to 13 feet is the usual
amount of heading up that river regulators are called upon to
effect. But there is a well-known work in Egypt — the Delta
barrage — ^which, with the help of a recently built subsidiary
weir below either section of it, now holds up 20 feet, each
work undertaking half the head. If a project contemplated so
considerable a heading up as this, the division of the head
between two separate works would probably be considered
advisable, and the Delta barrage principle be imitated. For a
single work it has hitherto been considered wise to limit the
head to 13 feet when the work has to be founded on the
ordinary sandy bed of a river. But the "Grand Anient" of
Madras, which is said to have been constructed sixteen hundred
years ago, and which was until quite recently in effective use,
had its crest 15 to 18 feet above the bed of the river, though
composed only of rough stone set in clay without mortar of
any kind. The Kistna weir, built in 1855, has its crest 16
feet above summer level and 25 feet above the deepest part of
the original bed.
In deciding upon the design of the river regulator, the effect
112 IRRIGATION.
that the obstruction, which it creates in the river channel, will
have on the flood discharge must be carefully considered. If
the backing up of the water, or "afflux," should be consider-
able, there may be danger of causing inundations in consequence
of the higher flood levels produced, and danger, perhaps, of
the flanks of the river work being turned by the flood water.
The solid immovable part of the regulator, which remains
through the flood, must not therefore obstruct so great an area
of the flood waterway as to affect the high water levels
inconveniently. In the case of the Egyptian barrages and
regulators of the French type, the obstruction offered to the
flow is slight, as the shutters which effect the heading up at
low supply are removed clear of the water during flood. The
design of the French types provides for the removal also of
the supports against which the shutters bear.
In India, where the regulator takes the form of a solid weir
called an anicut.^it has been found, as the result of experience,
that the afflux is not the only effect of a solid obstruction that
makes it desirable to limit the height of the weir. In the case
of anicuts of ordinary height, many examples of which exist
in India, the afflux in flood is not sufficient to be a serious
objection. But in several cases it has been found that the
obstruction of the flood waterway causes irregular silting up
of the river bed above the anicut, and that the summer channels
are inconveniently affected thereby. Sometimes on this account,
and sometimes from other causes, a sufficient discharge could
not be forced into the canals at low supply ; consequently, in
such cases, it has been found necessary to add crest shutters
along the whole length of the anicut to raise the summer level
still higher, so that the river water may flow into the canals.
These shutters are so designed that they may be laid flat
in the flood, and not cause any additional obstruction to the
• A critic objects to " the term ' anicut' as purely a Madras word, which
is neither used, nor even generally understood, in other parts of India." But
the Sone weir in Bengal was known as the " Dehri anicut," and the Sone
engineers were familiar with the term.
MEANS OF DRAWING ON THE SUPPLY. It3
flow. Profiting by the lessons taught by experience, the irriga-
tion engineers of India have recently shown a preference for
low weirs with crest shutters, and the later designs take this
form. The crest shutters are usually from 2 to 3 feet high, but
in some cases are 6 feet high.
An anicut is made up of the weir proper and of one, two, or
more groups of " under-sluices." These " under-sluices " are
regulating openings in the weir, divided up into bays, fitted
with some form of regulating shutters. They are sometimes
called "scouring sluices," a term to be preferred to the more
commonly used " under-sluices." The floor of the sluices is
at or about the level of the bed of the deepest channel of the
river at the site of the weir. It was expected by the original
designers that the control of the flood currents, which the power
of opening and closing the sluices would give, would make it
possible to maintain the deep channels of the river along such
lines as might be desired, and that silting up of the river bed
above the weir would be prevented. But the influence of the
under-sluices has been disappointing, and the expectations have
been only partially realised. In the case of the Sone anicut
in India, under-sluices were provided on each flank of the weir,
below the offtake of the canals on the right and left banks of
the riyer, in order to create a draw past the canal heads. There
were also added (but not without misgivings) under-sluices in
the centre of the weir, which were expected to prevent silting
above the weir and to maintain a navigable channel across the
river. They have done neither ; and so, as they were very
troublesome to manipulate, they have now, after being in use
for thirty years, been permanently built up.
The difficulty caused by the irregular silting of the river bed
above an anicut may be lessened in some cases by a judicious
selection of the anicut site. A straight reach of the river,
where the cross-section is constant and the velocity of flow
uniform, off'ers favourable conditions. A site where the river is
abnormally wide, though it may afford facilities of construction,
is not favourable to the prevention of irregular silt deposit. It
I. I
1 14 IRRIGATION.
would be better, if such conditions offer, to select a site where
the general width of the river is rather less than the normal
as the one most likely to be free from the silt trouble. The
increase of velocity over the weir itself, due to less length,
might necessitate somewhat heavier stone in the talus ; but, if
so, the expense would be balanced by the economy resulting
from the shorter length of weir. But, though the average rate
of flow would be greater in the shorter weir, the maximum
velocity might even be less, as the flow over the longer weir
would not be so uniform in consequence of the silt deposit
above it interfering with the even flow. It is irregular silting
that is objectionable as giving rise to currents which are not at
right angles to the line of the weir and which may besides have
locally a high velocity. Uniform silting against the weir along
its up-stream face and over the adjacent river bed is beneficial
as adding to the strength and impermeability of the work.
In all cases in which the bed of the river is sandy, the weir
should be built at right angles to the direction of the stream.
There are exceptional cases, where the river bed is rocky or
strewn with boulders, and the river velocity is high, in which it
may be advantageous to adopt an alignment inclined to the
stream. Figs. 29, 30, 33, 34, and 35 give cross-sections of those
weirs of the Indian type which have been selected as examples
of the different varieties of design adopted. The weir below
the Delta barrage is given as the Egyptian variety, the design
being based on that of the Sone weir, but having its own
points of originality. The different varieties are classified as
follows : —
(1) Weir with vertical drop on to impervious floor : to this
class belong the Narora, Burra, and Baiturnee weirs;
(2) Weir without drop, but with impervious floor sloping
downwards from the weir crest : to this class belong the
Chenab and Godavery weirs ;
(3) Weir without impervious floor or drop, but with slope of
stone with open joints inclined downwards from weir crest : to
MEANS OF DRAWING ON THE SUPPLY.
115
this class belong the Sone, Mahanadi, Brahmini, Kistna, and
Okla weirs, and also the Egyptian weir.
The Narora weir has been selected as an illustration of the
first class, for it has a record which is instructive. It was
originally built as in Fig. 29. A weir of this description, in
common with weirs of the other classes, has to guard against
the danger of the overflow scouring holes in the river bed along
the down-stream toe of the talus, and cutting backwards till the
main body of the work is reached and undermined. The deep
NARORA WEIR
AS ORiaiNAi.LY /CONSTRUCTED
PlQ 99
AS STReNQTHENED
FIQ 30
curtain wall along the down-stream edge of the floor of the
Narora weir was designed to meet this danger. But a curtain
wall in such a position does not give absolute security ; it is, at
best, but the second line of defence against the scour which may
threaten the stability of the work. The talus of heavy stones
is the first line of defence, and whenever any of this is displaced
in consequence of the scouring out of holes by eddies, or through
the sweeping away of the stones by the high velocity current,
the holes must be filled up and the slope re-made to its
original height, with still heavier stones than before if found
necessary.
i 2
1 1 6 IRRIGATION.
Another danger to which weirs in general are subject is
leakage under the weir main wall or floor, known as " piping."
When subjected to a head of water there is always, in the case
of weirs built in sand, movement of water under the weir from
up stream to down stream. But if the resistance encountered is
sufficiently great, the rate of flow is so low that the foundation
bed of the weir is not disturbed. Should, however, a run be
created in which the velocity of flow is high enough to carry along
grains of sand, by degrees the leak will increase until it undermines
the weir and causes its failure. The failures of the under-sluices
of the Mahanadi weir in 1886, and of the Chenab weir in
1895, were ascribed to this cause; and the Delta barrage in
Egypt suffered from the same defect in 1867. This form of
danger is aggravated by the scouring action of parallel currents
whenever they establish themselves along the front of the weir
from faulty alignment or other cause. Such action must be
guarded against by constructing long spurs at right angles to
the weir to guide the flow into the right direction.
But, besides these dangers common to most weirs, the form
of which the Narora weir is an example has two other forces
to resist. The one is the force of the water falling on to the
floor over the weir wall ; the other is the force exerted on the
under-side of the floor, tending to lift it, due to the pressure
developed when the weir is holding up a head of water. The
first is easily met by giving the floor sufficient thickness and
covering it with ashlar blocks.^ If the ashlar is properly
bedded, there need be no fear of failure in the case of a weir of
slight fall, such as anicuts have, in consequence of the action of
the water falling on its floor surface. But the other form of force,
which is applied to the under-side of the floor, is not so easily
disposed of, and its mode of action must be carefully studied.
The Narora weir is a useful example for consideration, for it
failed in 1898, and its failure has been the cause of much
fruitful discussion.
' bul see remarks on p. 141 concerning ashlar coverings.
MEANS OF DRAWING ON THE SUPPLY. 11/
The upward pressure, due to the head on the weir, decreases
in its transmission through sand in proportion to the distance
travelled. It is a maximum at the starting-point, and practically
nothing at the point where it finds an exit below the weir, pro-
vided that the floor is long enough to reduce the issue of
percolation water along the line of exit to a mere trickle. The
pressure at any point can, therefore, be found by drawing a right-
angled triangle with its base representing the path which the
water has to travel between the starting-point and the point of
exit, and with the perpendicular to the base representing the
head of water. The " hydraulic gradient " is then represented
by the hypothenuse of the triangle, and the pressure at any
point along the path of the water by the line drawn perpen-
dicularly from the corresponding point of the base to the
hypothenuse. If, for example, the path of travel is loo feet
and the head 12 feet, then at 25 feet distance from the starting-
point the pressure will be that due to a head of 9 feet, at
50 feet distance to a head of 6 feet, and so on. Thus it will be
clear that the shorter the path the steeper will be the hydraulic
gradient, and, therefore, the higher the rate of flow. The path
of travel is assumed to follow the face of the masonry, whether
it is horizontal or vertical. Assuming that the material offering
resistance to the flow is uniform throughout the path of travel,
the line representing the hydraulic gradient will be a straight
line.
Only a few days before the floor of the Narora weir was
lifted two pipes had been fixed in the floor in communication
with the .under-side at the points shown in the accompanying
sketch (Fig. 31), with the object of ascertaining the pressure by
direct observation, as some doubts were entertained concerning
the stability of the work. The insertion of the pipes had nothing
to do with the accident, as that occurred in a quite different
part of the weir. At the time of the experiment the head on
the weir was about 12 feet. The height to which water rose in
the pipes showed that, at a point about 13 feet from the
Ii8
IRRIGATION.
up-stream face of the weir wall, the upward pressure was that
due to a head of ii feet of water; and that 34 feet from the
same face the pressure was that due to a head of about 10 feet.
Such being the case, and the floor being only 5 feet thick,
matters would be critical when the river bed below should
become dry. Mr. Buckley, relying on an official report, thus
describes the giving way of the floor: " In March, 1898, some
350 feet of the floor of this weir was ' blown up ' by the water
NARORA WEIR
SHOWING OBSERVATION PIPES
FIG 3t
^, r*Lus
' 100 /OMg
Scalt of p I I I I I
pressure below it ... At the time of the accident a strong
spring burst through the floor at the toe of the crest wall, and,-
passing under the stone flooring, lifted it bodily over a length
of 340 feet to a maximum height of 2"23 feet. The weir wall
settled, in a length of 120 feet, about 3 inches, and the flooring
showed vertical cracks. The grouted pitching below the floor
was ' blown up.' Up stream of the part of the weir which was
damaged the apron had disappeared, and the wall was exposed
to a depth of 8 or 9 feet. Borings through the floor revealed
cavities below it extending to about 50 feet on each side of
the point of fracture." The original puddle up stream of the
weir wall had, previously to the accident, been scoured out,
MEANS OF DRAWING ON THE SUPPLY. ng
and had been replaced by block kankar. Consequently the
starting-point of underneath flow was against the weir wall
itself.
On the assumption that the floor of the weir was blown up,
it would appear that the upward pressure was too strong
for the floor, or the floor was too weak to resist the
upward pressure. There were two possible remedies : either
to make the floor strong enough by building on the top
of it, or to reduce the pressure under the floor. The latter
was the remedy adopted. The starting-point of underneath
flow was removed 80 feet up stream, and thereby not
only was the pressure under the floor reduced, but the
hydraulic gradient was considerably flattened out — conditions
favourable to stability and prevention of " piping." This
result was obtained by adding up stream of the weir wall an
apron of puddled clay 2^ feet thick, with its surface and up-
stream end protected from scour by a layer of pitching and a
bounding wall of kunkur masonry, as shown in Fig. 30. The
up-stream face of the weir was secured against the danger
arising from parallel currents by the construction of additional
groynes to act as guiding spurs. A dwarf wall, 3 feet high,
was added along the down-stream edge of the floor to form
a cushion of water below the drop of the weir wall. This
cushion would also have the effect, when the river bed below
the weir was dry, of adding weight to the floor, and of
counterbalancing 3 feet of the upward pressure.
The condition of things at the time of the accident, as well
as since the additions, is shown in Fig. 32. It will be seen
from the diagram that the upward pressure on the floor beJow
the drop has been reduced from loj to 6f , that is, to a pressure
due to 6| feet head of water, of which 3 feet is balanced by the
water cushion on the floor. So that there remains a head of only
3|feet to be resisted by the effective weight of the masonry floor
of 5 feet thickness (i.e., gross weight of floor less the weight of
water displaced).
120
IRRIGATION.
Another advantage of extending the impervious part of the
work on the up-stream side of the point where the heading up is
effected is, that the extension can be economically made of clay
puddle, as the upward pressure is more than counterbalanced
by the weight of water above. Clay puddle, with its surface
protected from scour, is as good as, or better than, masonry
in such a situation, provided that the junction of the puddle
and masonry is made absolutely secure against a leak. In
fact, if it were not for the necessity of resisting the pound-
ing and scouring action of the water down stream of the
DIAGRAM
TO SHOW PRESSURES ON FLOOR OF NARORA WEIR
80- ■
PUDDll
■»-«*«^---s*' ^--i8^--iah*--i»-'--»---
i( wIelLb
i "! 1 ? ■ £
i S iSi 5 '
KA8 ORIGINALLY CONSTRUCTED
AS .STRENGTHENED
I'll
SROUTEO
PITCHING
point of heading up, the impervious part of the work
might all be up stream. The full lines of the diagram of
the hydraulic gradient and pressures (Fig. 32) have been drawn
on the assumption that the water has to pass underneath the
deep curtain wells ; but as the interstices between wells,
especially circular ones, are difficult to make water-tight, the
path of the water probably passes between the wells. If the
depth of the wells is excluded from the path, the hydraulic
gradient will have a shorter base and will become steeper, and
the pressure on the grouted pitching be increased, as shown by
MEANS OF DRAWING ON THE SUPPLY. jgi
the dotted lines. It will be found that, with this correction,
the upward pressure at the point below the drop wall was that
due to lof feet head before the addition of the up-stream apron,
and is now 6 feet.
Although the cause of the failure of the weir may have been
wrongly ascribed in official reports to the " blowing up " of the
weir floor, still, had there been no failure, the observation pipes
had disclosed the critical condition of the floor and demonstrated
the necessity for the additions made.
There are several theories regarding the manner in which
this weir failed, and the local engineers decline to commit
themselves to a positive opinion. If, as seems to be generally
admitted, the grouted pitching beyond the floor was " blown
up," it is difficult to understand how the floor could have been
also " blown up." The blowing up of the pitching could not
have occurred after the blowing-up of the floor had reduced the
upward pressure on the pitching : nor is it likely that the floor
could have been lifted after the blowing up of the pitching had
reduced the pressure. An engineer of experience, who visited
the work not long after the accident, is of opinion that the
grouted rubble was first blown up, causing a loud report : the
rush of water through the hole, thus formed, scoured out the
sand from below the weir : the floor subsided into the cavity,
and, dislocation of the masonry resulting, a strong spring
issued at the toe of the crest wall, and the water under pressure,
finding its way between the separated layers of masonry, lifted
the ashlar covering of the floor. If this is the real sequence of
events, the moral is stated in conclusion No. 4 below.
A consideration of the diagrams. Figs. 31 and 32, leads to
the following conclusions : —
(i) That extension of the impermeable platform up stream of
the drop wall decreases the upward pressure on the floor below
the drop wall at the same time that it reduces the steepness of
the hydraulic gradient and, therefore, the rate of flow of the
percolation water ;
123 IRRIGATION.
(2) That extension of the impermeable platform down
stream has the disadvantage of increasing the upward pressure
on the floor below the drop wall, though the steepness of the
hydraulic gradient is favourably affected in the same way as by
an up-stream extension ;
(3) That for these reasons a curtain wall is well placed if
up stream of the floor, but badly placed if down stream, except
as a precaution against cutting back and undermining of the
floor; and —
(4) That it is a mistake to grout pitching on the down-stream
side of the floor, it being assumed that the water-tight floor
below the drop wall is made strong enough and wide enough
to withstand the impact of the falling water.
The case of the Narora weir has been examined at length,
as it exemplifies the principles on which the designs of recent
constructions have been based. There will be the less to say
about the other varieties of weirs.
The Chenab weir (Fig. 33), which has been selected as an
example of class (2) (no drop, sloping impervious floor), has a
similar history to the Narora weir. It failed from " piping,"
or leakage under the floor. As originally built, there was
only a triangle of stone pitching with a base of 24 feet
up stream of the main weir wall. Since the failure an apron
of surface-protected clay puddle has been added up stream
of the weir wall, as in the case of the Narora weir. It
is doubtful whether the addition of a line of piles or wells to
the clay apron is a proceeding to be recommended. Certainjy,
if they form deep water-tight curtains, they are more effective
in preventing " piping " than a corresponding length of hori-
zontal apron would be, as they alter the direction of the flow
and check the movement of the sand. 9 But if the intervals
between piles or wells are not perfectly filled and rendered
water- tigh t , they do more harm than good, as the unfilled inter vals
form vertical runs by which deep springs from the river bed
MEANS OF DRAWING ON THE SUPPLY.
123
find a free passage upwards to the under-side of the floor. The
subject of wells and piles will be further discussed in the next
chapter when considering the different methods of constructing
sub-aqueous foundations.
The third class of weirs, of which the Sone weir is selected
as an example, has no impervious floor, but is made of two
(sometimes three) parallel walls, generally founded on wells
sunk in the river bed. The spaces between the walls are filled
with rubble pitching, with a carefully packed surface of large
CHENAB WEIR
— ^-S i" 68
'^— -Impermeable 179' P/a/form
Zqtial IVidth 86*'
. - Kfr!^ .j^-a^ -'- - ^Sk£^~
+•10+- 46
-i i
WEIR
DELTA BARRAGE
-7" 0/0/ IVidlh 207'
..«io?-S7av^--:-v -^>-":":^:^^\
stones on end. The pitching is continued beyond the lower
wall. The cross-section (Fig. 35) gives the design and dimen-
sions of the Sone weir. In the case of this weir, 10 feet is the
total head. This is equally divided between the two walls, if
both are water-tight.
The Okla weir is remarkable for being constructed on the
surface of the river bed without any foundations below that
level. There are three walls. The maximum head on the weir
is 13 feet. The main wall holds up 4 feet, the middle wall
4 feet 3 inches, and the lowest wall 4 feet 9 inches ; that is,
supposing that the river below is dry and that all the walls are
124
IRRIGATION
water-tight. The percolation along the river bed, under each
wall, keeps the interspaces full of water, and so causes a division
of the head between the walls.
The Sone weir was the type which influenced the design of the
Delta barrage weir in Egypt. The cross-section given of the
latter (Fig. 34) is sufficient to show the design without explana-
tion. The manner of building the Delta barrage weir will be
described in the next chapter. It was important that the -weir
should be made as water-tight as possible in order that there
SONE WEIR
FIG 35 ;
might be no loss in summer when the water was standing level
with the weir crest. Mr. R. B. Buckley, who is an authority on
these matters and knows both the Sone and Egyptian weirs, has
stated in a discussion comparing the two weirs that, " while the
Sone weir fulfilled its purpose absolutely, it was not water-
tight," and added, " The subsidiary weirs on the Nile were the
most water-tight weirs that had ever been built."^ The core
wall, with its up-stream clay weighted with rubble, forms a
perfectly water-tight bar across the river. The utility of the
down-stream clay is doubtful, but, compressed as it is by a great
depth of rubble, it may help to preserve a tight joint with the
> Proceedings Inst. C.E., Vol. CLVIII., Part IV.
MEANS OF DRAWING ON THE SUPPLY. I25
river bed. At any rate, it removes the point where percolation
can first escape upwards to some distance from the core wall.
The footing wall is also given a water-tight joint with the bed
by means of up-stream clay, so that the maximum head on the
core wall is limited to the difference in level between the crests
of the two walls. The weir holds up altogether about 10 feet.
Probably it could do more if required, as it is considered by
some to be abnormally strong.
The heavy blocks of the weir tail are intended to stop cutting
back towards the footing wall. Should any holes be scoured
out along the down-stream margin, the blocks would subside
into them and check the action sufficiently to carry the work
safely through the flood. Before the next flood the holes would
be filled up with additional stone, and this process repeated
from year to year till a condition of absolute stability was
reached.
There is one other feature about this Egyptian weir design
which is worth attention. Down stream of the footing wall is
an arrangement known as " Beresford's filter," so named
because Mr. J. S. Beresford, CLE., was the first to suggest its
adoption in India. It is an inverted filter with strata of
materials of gradually increasing size, commencing with quite
small stone at the bottom. The filter allows the filtration
water to pass freely, but prevents the passage of sand. The
percolation water that travels under the work thus issues harm-
lessly. As a matter of fact, the dry rubble mass between the
two walls also acts as a filter bed, as the little percolation water
that at times flows over the footing wall has been observed to
be absolutely clear.
Tnere are no under-sluices associated with the Egyptian
weir, but a lock only for navigation. Neither has it any crest
shutters. The afflux in a high flood is almost imperceptible.
On the Indian weirs the crest shutters take various forms,
and much ingenuity has been expended on their designs. They
are for the most part raised by hand and secured in a vertical
126 IRRIGATION.
position by tie-rods fastened to the crest of the weir. During
the flood they are laid flat on the weir crest in recesses made to
receive them, so that the flood has a free passage. The shutters
of some designs are self-acting, and fall flat when the flood
reaches a certain level. Fig, 36 shows the pattern of crest
shutters erected on the Sone weir. The under-sluices have also
furnished a fruitful field for inventive minds. There are in use
many interesting contrivances for rapid opening when the flood
comes, some of which have been proved by actual practice to
be serviceable. One of the most fascinating arrangements,
designed by Mr. Fouracres, has been fitted to the under-sluices
of the Sone weir. But though this and others work well,
the tendency of evolution in irrigation methods of regulation
is the reverse of that which prevails in the animal world.
Complexity of structure is giving way to simplicity of design,
as being less subject to derangement and more reliable. The
system which now finds favour is that of wide vents, fitted
with gates which are lifted vertically by an overhead traveller
running on rails laid along girders supported on the tops of the
piers above high-water level. The gates, of which there are
usually two in each vent, run in cast iron grooves built in the
sides of the piers. Friction is reduced by means of rollers,
either fixed to the gates or arranged on the " Stoney " system.
Hitherto the vents have been generally 20 feet in the clear,
though, in Madras, "Smart's shutters" with counter-weights
have been erected in all sizes up to 40 feet in length by 12 feet
in height. " Stoney's shutters" are now being preferred to
"Smart's." Shutters 80 feet broad by 9 feet high, counter-
balanced and running in grooves on "Stoney's rollers," are a
feature of the design for a proposed regulator across the Penner
river in India.
The principle of Stoney's gates is shown in Fig. 37. The
gate bears on [groups of rollers mounted in hanging frames.
The gate moves freely on the rollers, and the rollers on the
recessed faces of the jambs, so that friction is minimised. It is
MEANS OF DRAWING ON THE SUPPLY.
127
easily understood that the sluice gate travels up and down at
twice the rate of the roller groups. Therefore, to maintain the
correct relative positions of gate and roller frame under all
circumstances, the two are connected by means of a wire rope
which, passing under a pulley at the upper end of the roller
frame, has its two extremities fastened, the one to the upper
FIG 37
^PS TREAM W.L.
STONEYS
GATES
DIAGRAM
SHOWING
PRINCIPLE
^\\\\\\^\m^>^
SECTION
TWPOUGH
GATC
SUrLOT .LU.CE
6TAUNCMINQ
PART
PLAN
0/ Pressure
edge of the gate and the other to a fixed point in the side of the
sluice. ^'Thus, as the gate is lifted 2 feet, for example, the
roller frame rises i foot.
In the various attempts that have been made from time to
time to devise a gate that would work with a rolling instead
of a sliding contact, the difficulty of obtaining a water-tight
closure against the two faces of the sluice has made itself felt.
128
IRRIGATION.
Mr. Stoney has overcome this difficulty in a way that is
simplicity itself. In the angle formed by the edge of the sluice
gate and the face of the jamb a turned bar, attached loosely to the
top of the gate, is allowed to hang freely. The pressure of the
water forces this " staunching rod " into the angle against both
the sluice gate and the jamb, and a perfectly water-tight joint is
thus secured.' The weight of the gate is sometimes balanced by a
counter-weight to increase the facility of moving it ; but,
whether counter-weights are provided or not, the gates are
manipulated with the greatest ease.
The system of vertically lifted gates sliding in groves was
THE DELTA BARRAGE
CHANNELS ^^^ '"° "
introduced into Egypt by Lieut.-Col. J. H. Western, C.M.G.,
when he was charged by the Egyptian Government with the
restoration of the Delta barrage. In this work the vents
are 5 metres (16 feet 5 inches) wide. The same system
has been imitated in the newly constructed barrages of Egypt
at Assiout, Zifta and Esna. This type of river regulator,
which has been classified above as the Eg57ptian type, will now
be described.
• " The Stoney Patent Sluice," by Ransomes and Rapier.
M^if£:d
^
'I
fe .iii.<itfe.Villt4aJ
MEANS OF DRAWING ON THE SUPPLY. 129
The Delta barrage is the prototype of the Nile regulators.
It is made up of two separate works, one on either branch of
the river close below its point of bifurcation. The main canals,
which distribute water to the Delta, take off from the pool
above the twin regulators. Fig. 38 shows in plan the general
arrangement of these works, and Plate VI. gives a general view
of the down-stream face of the regulator across the head of the
Rosetta branch. The Delta barrage^ has a history of much
interest to irrigation engineers. Its construction was com-
menced in 1843 by M. Mougel, its French designer, when
Mehemet Ali was the ruler of Egypt. The design to which it
was built is shown in Fig. 39. When the work was subjected
to a small head in 1863 and 1867, unmistakable signs of
failure appeared in the form of cracks and displacements, and
the barrage was forthwith put upon the sick list. The failure
was due to "piping." Runs below the floor were developed
under the influence of the head of water, and the sand of
the foundation bed was carried away by the flowing water till
the floor lost its support and settled down. The defects arose,
not so much from faulty design, as from careless construction of
the foundations. Worried by the impatience and impetuosity
of the Viceroy, Mougel Bey's workmen laid the foundation
concrete in running water, which carried away the mortar and
left loose stone, without any binding material, through which
the springs of the river bed had free passage. The design, if
faithfully executed, was not much at fault. The floor was
amply strong to resist the upward pressure due to the head,
but its breadth was perhaps deficient ; and the protection given
both on the upper and lower sides of the flooring was inadequate.
From 1867 to 1883 the barrage attracted attention by reason
only of its imposing superstructure, but it failed to produce any
impression by its performances, for it was weakest where
strength was most needed. In 1883 the Director-General
> "The Delta Barrage of Lower Egypt," by Major R. H. Brown.
Published by the Egyptian Government.
I. K
I30
IRRIGATION.
of Irrigation proposed to maintain the barrage as a liimple
bridge, and to provide for the irrigation of Lower Egypt by a
system of pumping stations. But in this year Egyptian
DELTA BARRAGE
CROSS SEOTJOW OF
FIG
MASONRY FLOOR
39
LBUPERSTRUCTURE
irrigation came under the control of Anglo-Indian reformers,
and the result, so far as the barrage was concerned, was to save
it from rejection, and to raise it to be the head of the corner
in the building up of a restored scheme of Egyptian irrigation.
The principle on which the design of the Delta barrage
restoration was based was the same as that which was followed
in the case of the Narora and Chenab weirs already described.
The path of travel for the percolating water was lengthened by
the addition of impermeable aprons of masonry up and down
stream, thereby increasing the width of floor from 34 metres
(ill feet) to 72J metres (238 feet), two-thirds of the increased
width being up st^ream.
But, besides adding to the width, it was necessary to lay a
sound water-tight surface over the old floor, which was cracked
and pierced by springs in many places and was otherwise
defective. The new covering was made of Portland cement
concrete 1*25 metres (4 feet) thick, over which was laid a heavy
pavement of dressed Trieste ashlar stone under the arches and
over that part of the down-stream apron where the action was
MEANS OF DRAWING ON THE SUPPLY. I31
most severe. In Plate VI. will be seen where the new floor cover-
ing was raised above the general level along the length that was
found most defective. A row of piles was added under the up-
stream apron — an addition which is now considered a mistake.
After the completion of these works, when the barrage was hold-
ing up water, springs appeared down stream of a certain length
of the floor. The line up stream along which the sources of these
springs lay was detected, and the flow stopped by dredging
out a shallow trench along the upper edge of the up-stream
floor extension and forming a clay apron in it under water, the
clay being consolidated by a submerged sledge and protected
from scour by a surface layer of cement concrete in sacks.
By means of this restoration work the barrage was made
capable of holding up a head of 4 metres (13 feet), as was
originally intended, and the consequent effect on the produce
of Lower Egypt was eminently satisfactory.
In the next chapter it will be told how the foundations of tht
barrage were further consolidated by means of cement grout.
After this last operation the maximum head held up was 4"35
metres (14 feet). While subject to this head the barrage
showed no signs of being unduly strained.
But, though the barrage had now been made to do no more
than its duty, it was thought unwise to subject a work of such
vital importance to as much even as 4 metres head, if there was
a practicable way of avoiding it. So supplementary weirs were
proposed to take some of the strain off the barrage. At first no
more than this was suggested, but the project grew during the
period of study beyond the original idea, and was eventually so
expanded that, instead of the associated barrage and weir
holding up 4 metres (13 feet) between them, the combination
was designed to hold up 6"20 metres (20 feet), the old work
being allotted 3 metres of this head instead of its original 4
metres. In this way a more perfect control over the distribu-
tion of water at the apex of the Delta has been obtained, not
only in summer, but also in flood ; while at the same time
K 2
1 32 IRRIGATION.
greater security has been gained. The design of the weir, beinq
of the Indian type, has already been discussed (Fig. 34). The
effect produced on the river levels, and the distribution of the
head between the barrage and its weirs, are shown in the
diagram (Fig. 40). The photograph, of which Plate VI. is the
reproduction, was taken before the construction of the weirs,
when the barrage was holding up 13 feet head of water. The
action of the weirs now ponds up water over the barrage floor
so that the talus stones are never visible. On the Rosetta
branch of the Nile the subsidiary weir is 1,500 metres (1,640
DIAGRAM
OF WATER LEVELS AT THE 0E1.T* BAHBAOE
(ye/ore aai after ctmstruction of thi
m, Weirs. FIQ ^0
L.W.L. WITHOUT WEIR \A- ^
~ "" .\~ T ^ K\ ..W.L. m POHO BETWEEW >
RACE AND WEIR j 1 ~n
W.L.wh;hout . weir\_ ^ _y.I k
W .L.
>. BELOW WtiR
yards), and on the Damietta branch 500 metres (550 yards),
down stream of the barrage, so that the weirs are entirely
separate works from the older construction.
Other instances of the Egyptian type of regulator have been
lately built at Assiout and Esna, in Upper Egypt, and at Zifta,
in Lower Egypt. As the design of the latter is practically the
same as the Assiout barrage design, but modified in certain
details as a result of the experience gained in building the Upper
Egypt work, the cross section of the Zifta barrage is selected as
an example of the most recent form of the Egyptian t5rpe of river
regulator. Fig. 41 gives the principal dimensions. It will be
MEANS OF DRAWING ON THE SUPPLY, 133
observed that the floor has a diminished thickness down stream
of the piers, as the hydraulic pressure upwards, due to percola-
tion, decreases towards the down-stream end of the floor, and
the floor surface beyond the piers is not subject to the pounding
of water faUing over the gates. The clay apron up stream,
weighted with rubble, forms an extension of the impermeable
floor, and removes the starting-point of the flow of the percola-
tion water to the up-stream edge of the clay. Down stream of
the floor is an inverted filter bed overlaid with the heavy rubble
of the talus. Up-stream and down-stream rows of piles, with
joints grouted up solid with cement, form continuous curtains.
ZIFTA BARRAGE
CROSS SECTION OF FLOOR
FIG 41
SUPERSTRUCTURE |
■ -4
ie-..~ Total- -Width 4- y— S«&'--,
I ^Impermeable Platfortn. \—Wa ^
! i.1« ftJt -^9-.< tSTii- i — — 87- + fi-*4-
if -I 69^ A
■^ Scale
MIN I I I 1 I T I I I I " Feel
The up-stream piles are useful in increasing the distance the
water has to travel, after starting from the up- stream edge ot
the clay apron, before it presses upwards on the under side of
the floor. 'The down-stream piles are not necessary to the
finished work, but they facilitated the laying of the concrete
platform, and were also a security against the material of the
river bed below the concrete being withdrawn by springs
flowing from under it to the pumps which kept the water down
during the construction of the floor. The down-stream row of
piles was therefore retained, but was made of less depth than
the up-stream line.
It was found during the construction of the Assiout barrage
134 IRRIGATION.
that the weak point was the line of junction between piles and
concrete, along which springs forced their way upwards. In
the Zifta barrage design the masonry floor was therefore
extended outwards for a short distance up stream and down
stream, to cover the heads of the piles, an arrangement which
would enable the springs to be dealt with and effectually closed
if they appeared.
The Zifta barrage was designed to hold up 4 metres (13 feet)
of water, which it proved, after construction, to be fully
capable of doing. But before it had been in use two years, the
advantage of holding up more than 4 metres (13 feet) was
recognised, and a subsidiary weir has been constructed down
stream to enable the heading up to be increased. This weir is
a more modest one than the Delta barrage weirs, but it is of
much the same design to a smaller scale.
With reference to the question of the future type of river
regulator that engineers in India may be expected to adopt, the
following passage occurs in a Manual on Irrigation Works,
compiled by Mr. B. P. Reynolds, Instructor in Civil Engineer-
ing, for the use of the students at the College of Engineering
in Madras, India. The manual is dated January, 1906, and
therefore may be assumed to be giving expression to the recent
thought of engineers in India, so far as the author of the manual
was acquainted with it: — "There can be no doubt that the
weirs of the future will be of the open type, raised little, if any,
above the bed of the stream and fitted with movable shutters
on the crest,; and since it is necessary that some kind of bridge
should be erected over them from which to work the lifting gear
of the shutters, it follows that these weirs practically become
regulators. In almost every case, except perhaps for very
broad rivers, the shutters will be of the lifting type ; falling
shutters, while useful for broad rivers, have the serious objec-
tion that once they fall the flood water must drop nearly or
quite to the level of the floor of the weir before they can be
raised again, while with lifting shutters the water can be held
MEANS OF DRAWING ON THE SUPPLY. I35
up to any convenient height and all excess safely passed."
The Zifta barrage is an embodiment of modern ideas as to the
principles on which a river regulator should be designed, and
it would appear from the passage quoted above that the Indian
type is likely to be modified in such a way that it may even-
tually differ by little, if at all, from the Egyptian type. The
existing barrages of Egypt are divided into bays of 5 metres
(16 feet 4 inches) width, and have their floor surfaces flush with
the bed of the river. With the facility of regulation provided
by Stoney's shutters the width of the bays could without incon-
venience be increased four or five times, as in the regulator
across the Penner river; and, if ample width of waterway
were allowed, there would be no objection to raising the floor
a little above the river bed with the object of decreasing the
height of shutter required to hold up water to the desired level.
Mr. Buckley (" Irrigation Works in India," p. 149) describes
the method of remodelling the Coleroon anicut in India. The
original weir proved in time to be not high enough. A new
"anicut" was therefore built, up stream of the old one, with
fifty-five 40 feet spans, regulated by lift shutters 4 feet high.
As the sill of the new " anicut " is 4 feet below the crest of the
old weir, the top of the shutters is only 2 feet higher than the
crest, and therefore, if the sluices in the old weir were to be
wholly closed, the new work would have only a 2 feet head to
support, while the old work would hold up 4 to 5 feet. This
combined work has, therefore, a resemblance to the Egyptian
Delta barrage and its weirs, but the order of construction of
barrage and weir was reversed. The new "anicut" of the
Coleroon combination is in fact, as Mr. Buckley states, "an
arched bridge, the water passing through it being regulated by
means of lift shutters." In other words, it is a river regulator
of the same type as the barrages of Egypt.
Reference has been made in the earlier part of this chapter
to the intention of the Egyptian Government in 1883 to adopt
pumping from the river as its only method of supplying Nile
136 IRRIGATION.
water for irrigation. For some years previously pumping
stations at Atfeh and Khatatbeh, in Lower Egypt, had been at
work lifting water from the Rosetta branch of the river for the
irrigation of the Western Province of the Delta. A contract
had been concluded with a company for the working of these
stations, the terms of which were modified in 1883 to provide
for an increase in the amount of water delivered into the canals
by the pumping stations. The new terms provided for a supply
of 2,000,000 cubic metres a day (818 cubic feet a second) at
Atfeh, and 2,500,000 cubic metres a day (1,022 cubic feet a
second) at Khatatbeh, at an annual cost of about ;f50,ooo.
This contract was to last till 1915. As the Delta barrage stood
condemned as incompetent to serve the needs of irrigation, it
was proposed to extend the same system of supply by pumping
to the whole of Lower Egypt at an initial cost of £700,000 and
an annual expenditure of £250,000. But fortunately for Egypt,
before a decision had been taken regarding this proposal,
Colonel (now Sir Colin) Scott-Moncrieff was entrusted with the
management of the irrigation of Egypt. He pigeon-holed the
pumping project, declared himself in favour of a restored
barrage, and forthwith took steps that led to its successful
restoration.
The total cost of the restoration was £475,000. About
£500,000 more was spent on the east and west main canals to fit
them for their work. It may be stated in round figures that the
barrage restoration project cost one million, and, as the pumping
project was estimated to cost £700,000, its actual cost would
probably have been also about one million. But when a com-
parison is made of the annual expenditure in each case, the dif-
ference is striking. The Delta barrage costs less than £10,000
a year to maintain and regulate, and without any further expense
is capable of distributing any increased supply that may be
provided to meet the demands of a growing area of cultiva-
tion ; whereas the annual cost of lifting the water by pumps
—estimated at £250,000 in 1883, before the development in
MEANS OF DRAWING ON THE SUPPLY. 1 37
cultivation of the past twenty years had taken place — would
increase with the quantity of water to be lifted, and fluctuate
with the price of coal. Moreover, it would be a risky thing for
Egypt, whose coal supply must come by sea, to be dependent
on imported fuel. In time of war the coal supply might be cut
off, and a coal famine, of two months duration only, would,
under such circumstances, be enough to seal the fate of the
growing cotton crop, worth £15,000,000 at present prices. The
barrage is undoubtedly the most reliable agent for Egypt to
entrust with her interests. It has, since its restorationj become
so efficient, and is so unmistakably the proper instrument for the
water distribution of the Delta, that the Khatatbeh pumping
station has been dismantled, and its engines and pumps trans-
ferred to another station which provides for the drainage of
low-lying lands in the north-west portion of the Delta. The
Atfeh pumping station is still maintained, as it is so situated
that it can assist in supplementing the summer supply by
pumping into the Mabmudia Canal the water that comes from
springs and percolation in the river trough itself, between the
barrage and Atfeh, when the Delta barrage is closed. This
source of supply has not been mentioned in Chapter IV. as it
is peculiar to Egypt, but, as similar conditions may arise else-
where, it may be worth while to point out the measures taken
in Egypt to utilise every available drop of river water in its
irrigation. By the time that the river discharge reaching the
Delta barrage has so far decreased that it is no more than that
required by thfe canals fed from the river above, the gradual
lowering of the barrage gates is complete. The leaks round
the ends and between the gates are then caulked with rags, and
the closure of the two branches of the river by the barrage
made practically water-tight. But below the barrage there are,
on each branch, some 200 kilometres (125 miles) of channel
from the beds and sides of which spring and percolation water
collects in quantity not to be despised. When the river
discharge is due to this source alone, the salt water of the
1 38 IRRIGATION.
Mediterranean invades the lower reaches of the river branches
and, mixing with the spring water, renders it unlit for irrigation
purposes. Therefore, in order to make this Spring water
available for irrigation, the engineers have, since the barrage
became efficient, adopted the practice of constructing tem-
porary dams, one in either branch some little distance from the
point where it joins the sea, with the double object of excluding
the salt water and of retaining the spring water. On the
Damietta branch this water is drawn upon by a number of
privately owned pumps, and on the Rosetta branch by a few
private poimps and by the Government pumps at Atfeh. More
than half of the supply, however, flows by gravitation into
canals irrigating low-level lands in the north of the Delta. The
quantity of water obtained during the summer by such means
from the Rosetta branch is generally about 100,000,000 cubic
metres, tiiough as much as 170,000,000 is reckoned to have
been obtained. The Damietta branch is calculated to similarly
supply 80,000,000 cubic metres.
The Atfeh pumping station is the only remaining Govern-
ment station in Lower EgjTpt which is worked in the interests of
irrigation.^ Its performances are, moreover, Umited to lifting
from 70,000,000 to 75,000,000 cubic metres during the summer
when the want of water is most felt.
But, though the irrigation of the Delta can be more
economically and efficiently done by a system of canals
depending on barrages than by pumping, there are certain
isolated areas in Upper Egypt which cannot be given perennial
irrigation without pumping. The Egyptian Government has
now erected pumping stations for East Giza, a tract of country
comprising about 46,000 acres Is^ing immediately to the south
of Cairo. As this land cannot be served by a perennial canal
on account of its isolation, there was no choice in the matter if
it was to be given perennial irrigation.
• The previously privately-owned Abu Menaga pumping station has been
taken over by tlie Government for the irrigation of 12,000 acres in the high
level province of Kaliubia, The prospective area to be served is 68,000 acres.
MEANS OF DRAWING ON THE SUPPLY. 139
In Upper Egypt there are some 200 pumps operated under
private enterprise by engines of an aggregate horse-power of
about 5,000. The largest among these are worked in combina-
tion with sugar factories, for the irrigation chiefly of sugar cane.
During the flood season they are relieved by the inundation
canals whenever these latter flow at a sufficiently high level to
give irrigation by " free-flow." The following are the five most
powerful stations.
Names of Sutions.
Horse power.
Area of Crop Irrigated,
Mataana .
150
1,500 acres
Armant .
350
3,500 „
Dabaya .
150 .
1,500 „
Naga Hamadi
500
5,000 „
Ayat
400
4.000 „
The lift in summer in Upper Egypt is from 8 to 10 metres
(26 to 33 feet).
There is an interesting venture, undertaken by a company,
to irrigate the Komombos plain in Upper Egypt. The soil of
the plain is derived from the high ranges which skirt the Red
Sea, and has proved to be productive when irrigated. But its
surface is some 20 metres (65 feet) above the summer level of
the Nile, and half that height above high-flood level. At this
remote point the price of coal reaches a high figure. There were
originally no local supplies of fuel, as the plain was bare.
Nevertheless a company applied for and obtained a concession
for the reclamation of the plain. Three pumps of 1,500 I.H.P.
each (giving each 1,000 horse-power in water lifted) hft water
about 24 metres (78 feet) for the irrigation of 20,000 to 25,000
acres. ^ To adapt the pumps to the varying conditions of river
level in flood and summer they have been sunk in a pit about
5 metres (16 feet) below the level of high flood. The success
of this undertaking depends upon the efficiency of the pumps
and good management, for. the conditions are formidable.
' A tourth pump of 2,000 horse-power has been added as a reserve.
140 IRRIGATION.
Sir William Willcocks in " Egyptian Irrigation " estimates
the number of pumps driven by steam power in Egypt at
7,000, with an aggregate I.H.P. of 57,000. This estimate
probably includes the pumps used for drainage purposes, which
will be referred to later.
It is rather a remarkable fact that in India, at the beginning
of this century, not an acre of land had been irrigated by
Government otherwise than by natural flow. In so large a
country, where all sorts of conditions exist, there must be land
so situated with reference to water supply that pumping must be
the most convenient, if not the only possible, way of irrigating it.
At length the Madras Government recognised this in a particular
instance, and approved a project known as the " Divi Pumping
Project," which provided for lifting water 10 to 12 feet for the
irrigation of 50,000 acres. The pmnping station consists of
eight 160-brake-horse-power Diesel oil engines and Gwynne
centrifugal pumps with discharge pipes 39 inches in diameter.
The cost of lifting a given quantity of water varies naturally
with the height it is raised and with the price of fuel. It also
varies with the power of the pumping stations, large installations
working more economically than small ones. The question of
cost will be examined when pumping stations for drainage
purposes are under consideration.
CHAPTER VII.
METHODS OF CONSTRUCTION.
Under the head of Construction the irrigation engineer has
to deal with works as big as the Assuan dam and as small as a
field outlet of a few inches diameter. Between these extremes
lie anicuts, barrages, canal head works, weirs, regulators, locks,
inlets, escapes, syphons, aqueducts and culverts. The common
characteristic of all such works is that they have to control the
flow of water in one sense or another, and therefore should be
built of materials that will resist the action of water. Other-
wise the ordinary principles of construction apply to them.
Good stone and brick in hydraulic mortar are the most reliable
materials. Iron can be safely used under water only on surfaces,
and for those structural parts which can be periodically
examined, so that any deterioration may be detected and made
good. Wood is only fit for use in temporary works and for
movable parts such as regulating apparatus. Some hydraulic
engineers of a robust faith may be found to put their trust in
ferro-concrete, or ciment-arme ; but they would do well to
remember that the process is too new for time to have concluded
its course of object-lessons. Those who are interested in seeing
what daring flights of design the advocates of this system are
capable of making should turn to p. 4 of Willcocks' " The Nile
Reservoir Dam at Assuan and After." , ^
In the figures illustrating the text the different descriptions
of masonry employed in any work, selected as an example, are
not distinguished one from another, as the choice of material
depends generally on local resources. In Chapter VI., p. 116,
.shlar was mentioned as a good covering for floors which are
142 IRRIGATION.
subjected to the impact of falling water, with the proviso,
however, that the ashlar must be properly bedded. In Mr.
Buckley's account of the failure of the Narora weir, quoted on
p. ii8, it is stated that a strong spring passed under the stone
flooring and lifted it bodily over a length of 340 feet Now
this could not have happened if the ashlar had been properly
bedded. There must have been unfilled spaces between the
ashlar covering and the floor below it, over which the water
pressure acted. Assuming that the vertical joints of the ashlar
were perfectly filled, and that the bed joints were imperfectly
filled, and also that the sub-ashlar spaces were in communica-
tion with the up-stream head of water by ever so small a channel,
the ashlar would be in danger of being lifted if the void spaces
and head of water were great enough to develop the pressure
necessary to overcome the weight of the stone. Supposing this
were so and the ashlar blown up, the remaining thickness of
floor, below the ashlar, might then be too weak to resist the
upward pressure of percolation water from below, and a failure
of the work would result by the rupture of the floor. In con-
sequence of this objection to ashlar, namely, the difficulty of
securing a perfectly uninterrupted bond between the ashlar and
the masonry below it, it is sometimes considered preferable to
dispense with an ashlar covering and to build the floor of
homogeneous material. The floors of both the Assiout and Zifta
barrages in Egypt were so built, the material of the floor above
the bed layer of concrete being of rubble stone in 3 to i cement
mortar throughout. All the stones were laid, as far as
possible, with their longest dimensions vertical, so as to obtain a
vertical bond. The masonry was brought up rough to floor
level, and was surfaced by laying fine concrete (2 stone, i sand,
I cement) between the projecting points of the rubble masonry.
All points of stones that projected above the correct floor-
surface level were dressed off with a stone-dresser's hammer.
So far as the foundations of most of the larger works are con-
cerned, the methods of execution are those which are imposed by
METHODS OF CONSTRUCTION. 143
the necessity of building below the level of lowest water. The
nature of the foundation bed, and the strength of the springs
over the foundation area, are important matters for considera-
tion in selecting the method to be adopted. But the price of
materials and facilities for obtaining them, as also the quality
of the labour market and the nature of engineering plant avail-
able, have to be taken into account. In the case of works to
be built on rivers which are in flood during certain months of
the year, or, in countries where a rainy season interferes with
construction, the duration of the working season also will influ-
ence the decision as to the most convenient method to adopt.
If the springs of the foundation bed are not expected to be
too powerful to be dealt with by the pumps which can be
brought to site, the ordinary method of getting in foundations
below spring level is to surround the area of operations by
banks so as to exclude the outside water (if the foundation pit
is not otherwise enclosed), and to get rid of the inside water by
pumping. It may sound a simple matter to surround the area
by banks capable of excluding the outside water, but in some
cases this operation is a very formidable one, on the success of
which the whole work depends. The enclosing banks should
be made well clear of the outside limits of the foundation area,
with a good margin to spare to allow for the earthwork settling
down to a broader base under the action of percolation, which
will increase as the inside water is lowered by pumping.
Interior space is also useful as affording room for stacking
materials, and for the erection of pumps with their wells. The
wells for pumps should be outside the extreme limits of the
permanent work. The pumps keep the water level in the
enclosed area low while the excavation of the foundation pit
is carried down to full level and the masonry of the foundation
is laid, so to speak, in the dry. As the bed on which the bottom
concrete is laid is often covered with several inches of water,
wherever springs are numerous, a liberal allowance of cement
must be used in mixing the concrete.
144 IRRIGATION.
One advantage of this method over others is that all
the work done is in sight at the time of execution, and
it can therefore be supervised the more efificiently. But it
has this disadvantage, namely, that, unless the springs are
intelligently and skilfully treated, defects in the foundations
will be created by the water forcing its way either under or
through the masonry. It happens sometimes that the super-
vising staff has not the experience necessary for successfully
dealing with the springs, but gains it as the work proceeds, so
that the first season's work is not without its mistakes.- The
golden rule to be observed in dealing with springs is that no
attempt should be made to stop them working until they have
been surrounded on all sides by masonry of sufficient strength
to resist their efforts to find a new outlet under or through it.
In the case of any work of similar design to that of the Zifta
barrage (Fig. 41), if the cement concrete, which forms the
bottom layer of the foundation platform, is advanced from one
extremity of the work in an even line towards the other,
regardless of what springs it may meet with, the springs will
form runs for themselves through the unset edge of the concrete
layer. And, as the work advances, more and more springs will
assert themselves in the same way, until there is a strong
out-flow along the advancing edge of the concrete, due to the
combined action of all the springs encountered ; except such as
may have forced their way side-ways to the lateral margins of
the concrete layer and have found for themselves a free outlet
there. The cementing material of the concrete will thus be
washed away as soon as it is laid, and runs wall be formed
under and through the foundation platform, which will be
sources of trouble afterwards. The way to avoid this is
carefully to locate all springs in advance of the work, and to
carry the concrete round them, but not over them. Thus the
springs will continue to work unmolested. But, in order to
prevent the discharge from them interfering with the progress
of the work elsewhere, their water must be confined and led
MKTHODS OF CONSTRtlCTlON. I45
away in pipes or channels of set masonry over or through the
concrete layer, and be allowed to flow until the sources are
completely surrounded by masonry too strong for the springs
to burst through They can then be forcibly stopped with safety,
and be rendered powerless to work harm , The methods of
dealing with springs vary in detail with the ingenuity of those in
charge of the work, but the guiding principle is the same in all
cases, namely, to offer no violence to the spring till sufficient forces
are marshalled and the investment is so complete as to make
any attempt to break out hopeless and submission inevitable.
The method of enclosing the foundation area and keeping the
inside water down by pumping was recently adopted in Egypt
for the construction of the Assiout and Zifta barrages, as it was
also some years previously for the restoration works of the
Delta barrage.
The Delta barrage restoration, carried out under the
direction of Col. J. H. Western, C.M.G., was a work of much
difficulty. The barrage, as has been already stated, consists of
two regulators, one across the head of each of the two branches
into which the Nile divides at the apex of the Delta. The
regulator across the Rosetta branch has sixty-one openings of 5
metres (16 feet 5 inches) and two locks, and is 465 metres (1,525
feet) long between the flanks. The regulator across the Damietta
branch had originally seventy-one openings and two locks
(reduced during the restoration to sixty-one arches and one lock),
and was 535 metres (1,755 feet) long. To carry out the restora-
tion work it was necessary to enclose half of one regulator at a
time, leaving the waterway of the other half unobstructed to pass
the river discharge ; so that the work had to be spread over
four seasons.' The working season between two successive
floods extended from November to June. Four months of this
time were occupied in making the enclosing banks and in
pumping out and clearing the area of work. At one point the
enclosing bank had to be made in a maximum depth of water
of 15 metres (49 feet). When the pumping had lowered the
I. L
t46 IRRIGATION.
inside water sufficiently to allow of the masonry work being
carried on, the head of water against the up-stream bank was
5"25 metres (17 feet). As the river bed was sand, so great a
head naturally gave rise to strong springs inside the enclosure,
not only outside the limits of the tarrage platforms, but also,
in consequence of original defects in construction, through
cracks and runs in the floor itself. In one instance a crack
had opened out into a fissure 4 inches wide for a length of
about 13 feet. According to the report of the resident engineer,
Mr. A. G. Reid, " where cracks of this sort occurred they were
staunched as follows : the broken floor was cleared of debris
bit by bit and covered at once with sand to a depth sufficient to
keep down the springs. It was then surrounded at a distance
by concrete laid after thorough clearing on the sound floor and
carried up to a level at which the springs could not break
through it. The concrete was then pushed on inwards until it
was stopped by the flow of water. When this occurred the
sand was carried away as deep as possible, and rubble masonry
laid in cement mortar was built on the sand, a trench about 5
metres wide being left coinciding with the crack in the floor.
Concrete metal was laid a few inches deep, and on it a pipe 2
metres longer than the crack, closed at one end and perforated
with half-inch holes along its under half-circumference for so
much of its length as coincided with the crack, was securely
built into the new masonry for its imperforate length. An
outflow drain was left in the masonry in the prolongation of
the pipe, and the water from the broken floor was thus passed
through the pipe to the pumps. When the masonry had set,
the pipe was covered in with masonry laid in cement gauged
neat, and the whole then raised to a safe height. The end of
the pipe was afterwards closed with an iron plate and the
outflow channel built up."
The manner of dealing with the springs met with in the
worst opening of all, where it was found necessary to build the
new floor, overlying the old, with a surface some 3 metres
METHODS OF CONSTRUCTION. I47
(10 feet) higher than that of the original floor, is thus described
in the same report : " The springs under this arch were
numerous and prevented the water being got down below
2 metres above floor. They were closed by the aid of iron
pipes. The floor having been cleared of debris, silt and rubbish
as far as possible, ordinary cast iron pump pipes, 6 feet long,
were put into place, one vertically over each spring, and
concrete was tipped to water surface round them and over the
whole area of the floor. Whilst this was being done, the water
coming through the pipes was led away to the pumps in
troughs and by chcinnels previously prepared. When the
concrete had set for six days, a trench i metre wide and
extending from pier to pier was dug through the concrete down
to floor level, a site having been chosen which was, as far as
could be judged, sound. The floor was thoroughly cleansed,
and the trench was then filled in vnth concrete laid in layers
and rammed. The object of this was to make a water-tight
diaphragm extend from the old to the new floor, and thus to
prevent creep of water between the two. The pipes were then
filled with finely broken concrete metal and closed by quarter-
inch iron plates bolted on to their flanges, indiarubber packing
rings being used to make the joint tight. The whole floor was
then concreted over to the necessary height and the ashlar
face laid."
But the greatest source of trouble were the numerous springs
which found their way upwards between the piles of the original
rows of piling within which the floor had been built. Eaph
separate jet had to be led into a pipe of suitable size surrounded
with masonry, ind the pipe closed and built over after the
masonry had set. As the manner of dealing with springs is of
such importance, the soundness of foundations depending on
their successful treatment, Sir William Willcocks' description
of the means adopted to imprison the springs along the old
sheet piling of the barrage is worth quoting (" Egyptian
Irrigation "). See Figs. 42 and 43.
L a
148
IRRIGATION.
«
' I. Vertical Pipes.— The spring was dug out to a depth of,
say 30 centimetres below the surface of the old masonry, and a
vertical tube of from 5 to 10 or 15 centimetres diameter, accord-
ing to the quantity of the water, was inserted. The hole was
then filled up with ballast round the tube. This tube was
drilled with holes on the lower half of its length, while at the
upper end were cut the threads of a screw, so that a cap might
METHODS
OF CLOSING SPRINGS
SECTION
A
FIG
PLAN
METHOD
4-3 BY
HORIZONTAL PIPES
D E F
1 t t
eventually be screwed on. Round the pipe, and removed about
10 centimetres from it, a ring of brickwork in stiff clay was
built, open on one side ; the cement masonry was then brought
up from A and B till it was flush with the brickwork in stiff
clay, and was allowed time to set. When set, the brickwork
in clay was removed, and the space between the pipe and the
cement masonry was filled up with cement mortar, or concrete
or brickwork, an open space being still left on , ne side to allow
METHODS OF CONSTRUCTION. I49
the water coming up through the ballast to flow freely away.
When the cement mortar had thoroughly set, and was strong
enough to prevent springs working up through it, the opening
was quickly shut up with dry cement and cement mortar, and
weighed down, and the water began to flow freely through the
top of the pipe. When the cement closing the opening had
thoroughly set, the cap was screwed on the pipe and the whole
built over.
" 2. Horizontal Pipes. — The pipe in this case was drilled with
holes on half the circumference of half the length, i.e., on a
quarter of its surface, and was laid horizontally in a trench,
with the holes over the spring, which had already had ballast
strewn over it. The ballast was spread round half the pipe to
the axis B C. At E F a ring of brick in stiff clay was built
round the pipe, and at D E cement masonry round the pipe.
When the masonry at D E had set thoroughly, the brickwork
in clay was removed and replaced by cement mortar or brick-
work, while the space from B to C was covered with cement
mortar and masonry, and the water allowed to flow down the
pipe C B A. Great care had to be taken that a hand pump
kept the water at M always lower than the top of the pipe,
until the masonry above B C had thoroughly set. When the
masonry had set the cap A was screwed on, and the whole
space carefully built over in cement masonry."
The Assiout barrage, in Upper Egypt, spans the undivided
river as a regulator with iii openings of 5 metres (16 feet
5 inches) each and a lock, making up a total length between
abutment faces of 820 metres (2,690 feet). The laying of the
foundations was complete in three working seasons, a different
section of the work being enclosed each season, while the river
discharge was allowed to pass in the other sections. The
maximum height of the enclosing bank was 9*8 metres
(32 feet 2 inches). The head of water against it, when the
inside water had been pumped down to the required level.
I50 IRRIGATION.
varied from 4*70 metres (15 feet 5 inches) to 6'25 metres
(20 feet 6 inches). The bed of the river was sand, and the
whole foundation bed was aHve with springs. The most
suitable pumps for unwatering the foundations were 12-inch
direct acting centrifugals ; larger pumps were found unwieldy,
and smaller pumps, though useful for small areas on account of
their portability, proved unsuitable for use as main pumps. At
one time there were seventeen i2-inch, two lo-inch, six 8-inch,
and three 6-inch centrifugal pumps at work. The main pumps
were mounted in pairs on circular brick wells, 5 feet ill
diameter, sunk to a suitable depth just outside the line of
the pitching, and sealed at the i)ottom with concrete plugs.
Apertures to admit the water to the wells were made in their
sides at successively lower levels as the water level in the
foundation pit was reduced.*
The springs were dealt with in various ways, in accordance
with the principles laid down above. But the final closing of
the pipes, to which the springs had been confined, was not
done as at the Delta barrage. Provision was made for screwing
on other pipe lengths to a height of 5J metres (18 feet) above
the floor, so that, when the masonry had set, each spring mi-^ht
be forced backwards by a column of cement grout, and any
run or cavity created by the flow of the spring be filled by the
groul. As the springs were so numerous, causing an outflow
at the advancing edge of the concrete, it was frequently neces-
sary to stop any further advance and to recommence the work
at a fresh point some distance ahead, whence the concrete was
carried back to meet the arrested portion. Large openings
were temporarily left along the line of meeting as vent-holes for
the springs, which were then controlled and finally extinguished
by the employment of perforated pipes and cement grout under
pressure.
It is now recognised that the use of sheet-piling of the ordinary
' "The Barrage across the Nile at Asyut," by G. H. Stephens. Pro-
ceedings InstC.E., Vol. CLVIII., 1904.
METHODS OF CONSTRUCTION.
ISI
description to form curtains is a mistake, as experience gained
at the Delta barrage and elsewhere has taught that the unfilled
joints form so many leads to bring deep-seated springs to founda-
tion level, while, in consequence of these joints, the advantage
of a continuous deep curtain wall is lost. To obviate these
objections a special form of pile, which provides for the complete
CAST IRON PILES
SIDE ELEVATION
no 44
1
1
\
-)
o
t-
" "~\ ' r "~
?S.
I o-z
■?>
^^■
i 3\
PLAN
ENLARGED CROSS SECTION
7i^
fT
filling of the joints with impervious material, was adopted at
Assiout and Zifta. This pile is of cast iron, with a tongue
and groove arrangement by which one pile locks with another.
The groove is deeper than the length of the tongue, so that,
when two piles are locked together, there remains a space
between the end of the tongue and the back of the groove, into
which a small tube can be inserted (Fig. 44). After the piles
152
IRRIGATION.
are driven and the pile-driver has advanced to a safe distance
a tube is introduced into the groove space and water turned
on under a head. The jet of water clears out the sand in the
joint, and, as it does so, the nozzle of the tube descends to the
bottom of the joint. The water is then turned off and cement
grout substituted (Fig. 45). The tube, with its nozzle, is then
.GROUTING APPARATUS
FOR PILE JOINTS
Sca/e of liiJiJiiiiiii
±
Feel
r IQ 43
QROUT TANK
TAP FOR
WATER
(r^
TAP FOR OnOUT
gradually lifted out of the joint, leaving it full from top to
bottom of cement grout, which in a few hours sets hard enough
to resist the strongest spring. In this way a continuous curtain,
without open joints, is obtained along the line of piles.
The piles are driven as soon as the excavation is sufficiently
advanced for the pile-drivers to get to work, so that the piling
is complete before the bottom layer of the excavation is
cleared.
METHODS OF CONSTRUCTION. 153
The disadvantages of putting in foundations with strong
springs in action over the foundation bed have caused other
methods to be resorted to. The system which makes use of
compressed air is well suited to subaqueous work in which
depth of foundation, but not continuity, is required. The
sinking of cylinders, for instance, to act as foundations for the
girder supports of river bridges is frequently effected by this
method. But it is not so conveniently applied to the con-
struction of works which have to withstand a head of water
and require continuous foundations of unvarying depth without
intervals. Moreover, the system requires special plant of a
somewhat complicated order, and trained labour skilled in the
process, as there is much danger attending its employment by
untrained hands.
In India the method of getting in foundations by well-
sinking is in favour, and has been repeatedly employed with
much success. Where a curtain wall has to be formed in sand
or silt below spring level, it is most unwise to attempt to get
it in by lowering the water by pumping below the general
foundation level. Well-sinking is one method of avoiding the
necessity of doing so. A group of wells is also often sunk to
provide extra support for heavy lock walls, piers, or other parts
of the superstructure requiring greater depth of foundation
than is given to the lighter portions of the work. Well-sinking
may be carried out with the help of compressed air, but it is
usually done by excavating the sand or soil from the interior
by ordinary dredging plant. Wells may be circular or
rectangular. Curbs with sloping under-sides and outside
cutting edge are first bedded in the sand or soil at the natural
water level, or at the level to which it may be judged con-
venient to lower the water by pumping. The wells are built
on the curbs, and the masonry given time to set. They are
then weighted, and the sand dredged from within by special
plant, so that the wells gradually sink below water level as the
excavation continues. More height is added to them (if not
1 54 IRRIGATION.
originally built to full height), and the sinking is continued
till the bottom of the well has reached the required depth.
Cement concrete is then lowered to the bottom of the well, and
a plug of 4 or 5 feet thickness formed ; or the plug may be
made by cement grouting if the water in the well is allowed to
stand at spring level while the grouting is being done. When
the plug has had time to set the interior water is pumped out,
and the well filled with ordinary concrete, or even simple sand,
as the interior core does no work. The intervals between wells
are then cleared out as far as possible and filled with concrete.
The superstructure is afterwards built on a platform covering
the wells.
In the construction of the Sone weir in India, for example,
well-sinking was extensively used for the foundations of the
weir walls and under-sluiees. The under-sluice piers and the
entire floor of the under-sluices (which is 537 feet by 123 feet
in area) are founded on rectangular blocks or wells, generally
8 feet square, which are sunk all over the area to a depth
of about 8 feet ; the blocks under the piers are longer and
deeper. The wells are filled with concrete and covered with
masonry topped with ashlar 18 inches thick (Buckley).
An excellent example of the use of wells for foundations is
' furnished by the new Nadrai aqueduct in India (see Fig. 60,
Chapter IX.). The piers which carry the aqueduct are founded
on wells sunk 52 feet below the bed of the lower channel. For
such foundations as these well-sinking is a most useful and
efficient system.
The sinking of foundation wells is sometimes a troublesome
and tedious operation, especially if the supervising staff and the
labour employed have not acquired skill by previous experience.
What to do, and what not to do, to ensure that the wells may
sink vertically and uniformly, is only to be learnt by actual
practice.
The great objection to the use of wells for the foundations of
a weir core wall, or for a curtain wall of a work which is
METHODS OF CONSTRUCTION. 155
subjected to a head of water, is the difficulty of filling the
intervals between wells so thoroughly that they may be water-
tight. The filling seldom reaches to the full depth of the wells,
and if the wells should have sunk out of plumb, as they often
do, the clearing of the interspaces, and therefore the rendering
of them water-tight, becomes almost an impossibility. For
this reason cast-iron piling with grouted joints was preferred
to a line of wells for the curtains of the Assiout and Zifta
barrages, and not for this reason only, but also because the
piling can be executed expeditiously, and the well-sinking
cannot. Time is required to construct the wells, to allow for the
masonry setting, to sink thfe wells, and to close the intervals
before the concrete of the floor can be commenced. With
cast-iron piling it can be arranged that the piles shall be at site
before the excavation is ready for them, and that they shall be
driven in advance of the final clearing of the foundation bed,
without causing any delay iii the commencement of the laying
of the concrete.
Wells were recently used in Egypt to form an up-stream
curtain wall to a new head built to the canal which takes off
from the Nile at Cairo and flows to Ismailia, carrying the
water supply of Suez and Port Said. The foundations of this
work were as treacherous as they could be, and, as the new
work was to replace two others that had successively failed, it
was highly desirable that there should not be a third failure.
The curtain line of wells was sunk 575 metres (ig feet) below
floor surface, or canal bed level. To get the full benefit of this
depth of curtain, it was necessary to arrange for a water-tight
closure of the intervals between the wells to their full depth.
Piles, made of half-inch steel plate stiffened with T irons, were
driven outside the wells to close the intervals (see Fig. 46).
These piles, though flexible to a certain extent, could not be
expected to lie so close against the masonry of the wells as to
produce a water-tight joint. So, in order to staunch the joints
between the piles and the wells, a pair of pipes was sunk in the
■56
IRRIGATION.
well intervals, one pipe lying in each of the angles formed by
the pile and the faces of two adjoining wells. The length of pipe
below the floor foundation level was perforated, and the pipe
was so placed that the perforations faced the angle between
pile and well. The pipes were sunk by means of a jet of water
playing on the sand at the ^ot of the pipe from inside the pipe
WELL INTERVALS SHUBRA
FIG 46
IROa 8HECT PILI
SECTION ON AB
Itself. When sunk to the required depth, the pipes were filled
with sand to ensure the exclusion of cement grout when
grouting the floor. In that operation (which will be described
later) the cement grout encircling the pipes made a water-tight
joint with the piles and wall of masonry outside the piles, so that
the well intervals were made absolutely water-tight from the
bottom to the top of the grouted floor, above which it was of
METHODS OF CONSTRUCTION. 157
course easy to build them up solid. There remained the depth
of interval below the grouted floor to render water-tight. After
the foundation pit had been laid dry by pumping, subsequent
to the operation of grouting the floor, the staunching pipes
were cleared of sand by means of a jet of water, and were then
filled with grout after the manner of grouting up the joints of
the cast-iron piles before described. It was found in every case
that the two pipes of a pair were in communication below the
grouted platform in which their upper ends were embedded, as
the grout, poured down one pipe, was observed to rise in the
other. The fact observed, namely, that these pipes were in
communication with each other under the grouted floor, makes
it almost certain that the arrangement has secured a continuous
water-tight curtain wall down to the bottom of the wells along
the whole of the up-stream edge of the floor.
There is yet another method of getting in foundations below
water. Cement, used in the form of grout, for binding
together materials under water, had been used successfully in
breakwaters and other constructions by different engineers
before the system received its most notable application in the
construction of the subsidiary weirs below the Delta barrage of
Egjrpt. In discussing this method it will be convenient to
describe first the practice as exemplified in the building of
these weirs, and to state afterwards what principles must be
followed. The object of the weirs has been already explained
in the preceding chapter, and the design is given in Fig. 34.
The core and footing walls up to the natural level of the water
in the river during the working season, and also the foundation
of the locks associated with the weirs, were formed under water
by the cement grout system. The manner of proceeding
was as follows : —
The river level in the branch selected for the season's work
was lowered as much as possible by shutting down the gates of
the Delta barrage up stream of the weir site, and thus diverting
all the river discharge into the other branch. A trench was then
1 58 IRRIGATION.
dredged across the river bed to dimensions and levels corre-
sponding with the foundation bed of the weir and its lock, as
shown on the designs to which the work was to be built.
Along this trench the two walls of the weir were formed of a
continuous succession of blocks from one side of the river to
the other by means of bottomless boxes put together in the
dredged trench with the help of floating plant (Fig. 47).
The boxes, being formed, were lined with sacking by the help
APPARATUS FOR FORMING
GROUTED BLOCK?*
Scale
f y ' 1
W L.
fiC 47
BARGE
Sbfi. Horizontal Beams
of Box Frames
of divers, in order to make them cement grout-tight, though not
water-tight. Four perforated pipes were next fixed vertically
at equal intervals along the centre of the box. This done, the
boxes were filled up to a little aboye water level with rubble of
all sizes that a man could carry, and unperforated pipes were
inserted into two of the perforated pipes, reaching almost to the
bed of the river which formed the bottom of the box. Funnels
having been fixed at the top of these inner pipes, cement grout
was poured down them. Above each of the other two alternate
METHODS OF CONSTRUCTION. 1 59
pipes was arranged a stand carrying a simple grooved wheel,
over which a string ran, having at one extremity a ball so
weighted that it sank in water and floated in the cement grout
at the bottom of the perforated pipe, and at the other
extremity a small weight just heavy enough to keep the string
taut. As the grout rose in the box the float in the pipe rose
with it, and the small weight, moving in correspondence down
a scale fixed to the stand, registered the amount of rise. When
the grout had risen 2 or 3 feet the inner pipes and recording
stands changed places, and grout was poured down the second
pair of pipes till the gauges over the other pair recorded a
further rise of 2 or 3 feet ; whereupon inner pipes and recorders
changed places again, and so on till the grout had mounted to
the top of the stones, displacing all the water in the box. As
the sea of grout rose from below, the inner pipes were gradually
shortened by successively unscrewing the short lengths of
which they were made up. The object of this was that the
fresh grout, being delivered just below the surface of the rising
grout, might not disturb the lower layers and interfere with the
process of setting. Cement grout is twice as heavy as water ;
consequently the grout, if delivered below the water, would
remain there, and would displace the water simply by its
gradual rise from below. To permit of the ready escape of the
water, vents were made in the sides of the boxes just above the
level of the water outside.
If the cement grout had been poured directly into the
perforated pipes, each bucket of grout would have had to fall
through water, and have at least suffered in quality, if it had
not been altogether " killed " by excess of water. By using an
inner unperforated pipe, with its lower end just below the sur-
face of the rising sea of liquid cement, a continuous column of
grout was added to the previous mass without any further
admixture of water. This is an important point to pay atten-
tion to if this method of construction is imitated elsewhere.
Another important condition is that the grout must be of neat
l6o IRRIGATION.
cement, without the addition of sand or other foreign material .
for if ^a mixture is made of substances of different specific
gravities, the constituents will, in the liquid form of grout,
separate from each other under the action of gravity, and form
distinct strata before the setting properties of the cement have
had time to prevent the segregation.
As soon as the cement grout had risen in the box high
enough to envelop the top stones, or slightly higher than the
water outside the box in the river, the scum was cleared off,
small stone was bedded in the surface grout, and the box and
its contents left alone till the following morning, when it was
found that the block had set sufficiently to stand by itself.
The parts of the box containing it were then cast loose and
moved forward to form the next block, and so on across the
river. Work was started on the core wall foundations at
several points along the line simultaneously by the different
rafts fitted up for the purpose. At each point of starting the
first box formed was four-sided. On the completion of the
first block one end of the box was removed, and the next and
subsequent boxes were made with the three remaining sides,
the block last formed closing the fourth side. The upper part
of the core wall above water level was then built in the dry,
and the clay, rubble, and apron blocks put in place.
Plate VII. shows the west weir under construction. The
wall on the left is the lower part of the core wall which was
formed by grouting, the water level having sunk since the near
blocks were made. The wall on the right, appearing just above
water level, is the footing wall. The near cross-wall is a con-
necting wall which, in its finished state, will form a toe to
support the shore abutment slopes ; the farther cross- wall, of
which the closing block is being formed, is the first of four
made at intervals of lOo metres to divide the weir into compart-
ments. Beyond that is an interval through which the reduced
discharge of the river is allowed to pass. On the far side of
the river the floating plant is at work forming the blocks of the
METHODS OF CONSTRUCTION. l6l
distant lengths of the two walls, which will later on be
connected across the central channel with the walls on the near
side. The depth of water against the core wall at the time
of taking the photograph was 20 feet, and against the footing
wall 10 feet.
The dimensions of each block made along the core wall
trench were 10 metres long by 3 metres broad and 7J to
6 metres high (32 feet 9 inches by g feet 10 inches by 24 feet
7 inches to ig feet 8 inches) ; that is, each block was about half
the size of a two-storeyed cottage. These blocks were formed
wholly under water.
The proportion of cement to the quantity of masonry formed
by this method is 37 per cent., a high figure for concrete; but
the rapidity and certainty with which the work can be executed
produce economies under other heads of expenditure, and the
results obtained are so perfect as to justify the employment of
this system, even if it be comparatively costly, wherever
perfection in the quality of the work and rapidity of construction
are desired.
As the method of cement grouting was adopted for getting in
the sub-aqueous portions of the weir proper, so as to avoid the
difficulties and disadvantages of dealing with springs which are
encountered when the method of unwatering the foundations is
resorted to, it seemed desirable and consistent to apply the
same method to the lock foundations, an undertaking which
had never been attempted before. The floor surface of the
finished lock would be below the low water level of the river,
so that the grouting of the foundation could not be continued
till the grout rose to water surface, as in the case of the core
wall blocks, but had to be arrested when the grout had risen to
a level 2^ metres (about 8 feet) below the water surface, j The
manner of execution was as follows : The foundation bed was
first dredged out to the necessary level, which was 4J metres (say
15 feet) below low water level. Two parallel walls (see Fig. 48),
bounding all the lock area on either side, were then formed by
I, M
1 62
IRRIGATION.
the same system as that adopted for the foundations of the
core wall, and with the same plant. The rectangle of which
these walls formed the sides (lOo metres by 17 metres, or
328 feet by 56 feet, in the clear between the walls) was then
closed at the two ends by sheet piles supported by horizontal
beams which were kept in place by pi'es driven a short
GROUTING METHOD OF
GETTING IN FOUNDATIONS
HALF CROSS SECTION OF LOCK
FIO 48
55Sr?Fw^
f* INNER PIPE
S^JQAi^felSi ^ t^^kX:!^^
SECTION OF ONE END WALL
-FOUNDATION
^^^^
distance into the bed of the river and tied at their tops to the
side walls already made (see Fig. 49). A staging was then
constructed across the enclosed space from side wall to side
wall, the perforated pipes having been first fixed in place about
3i metres (loj feet) apart all over the area. The pipes were
fitted with iron brackets to make them serve as upright sup-
ports for the staging. Two metres depth of rubble, concrete
METHODS OF CONSTRUCTION. 163
metal and pebbles were then thrown in to form the floor
foundation. At about i metre distance from the two ends
of the lock area a second interior line of sheet piling had been
arranged with its lower end below the level to which the
2-metre layer of rubble would come (Fig. 49). All the sheet
piling was lined on the inside with sacking to prevent the
escape of cement grout between the joints, in the same way as
in the boxes. When the 2-metre depth of floor material had
been deposited, as ascertained by sounding rods, grouting
commenced at one end of the lock and continued till the
other end was reached, the level to which the grout rose being
noted by the float and gauge arrangement as used on the boxes.
When the 2-metre layer had been given time enough to set, the end
spaces were filled up with stone and grouted. After three days'
interval the enclosed space was pumped out, and the grouting
was found -to have formed a perfectly sound floor without the
sign of a spring in it. The rest of the lock floor and walls was
built in the dry in the ordinary way after clearing and cleaning
the surface of the grouted platform.
The advantages of this system of cement grouting are that
the springs never get a chance of troubling, and the sub-aque-
ous work constructed by its employment is perfect in quality
and of a strength more than sufficient. No expensive plant is
required and no skilled labour, except only a few carpenters
and mechanics to prepare the parts of which the boxes are
formed, and a few intelligent supervisors to direct the putting
of them together. The system has also the merit of rapidity of
construction. The objection to it is its costliness, though much
of the expenditure in cement is balanced by economy in staff
and in all the extra outlay which accompanies a prolongation
of the period of construction.
The use of cement grout for the construction of the Delta
barrage weirs was preceded by a remarkable operation on the
Delta barrage itself carried out with the help of cement grout,
in imitation of similar work done some years previously
M 2
t64 irrigation.
at the Hermitage Breakwater, Jersey, by the late Mr. W. R.
Kinipple. ^ It will be remembered that the bottom layer
of the concrete platform on which the barrage rests had its
cementing material washed away during construction by springs,
leaving loose concrete metal behind. This defective layer, and
the original unsound floor above it, was covered over and cut off
from communication with the river water by Colonel Western's
enveloping additions to the floor. But the loose material still
remained, affording a passage of practically no resistance to the
travel of the percolation water along that length of its path
which followed the under-side of the original foundations. It
was felt that, if this bottom stratum of the old floor could
be made impermeable, additional security would be obtained.
The introduction of cement grout under pressure to the bottom
layer, with the view of filling the interstices of the concrete
metal with set cement, was the method selected. The accom-
panying diagrams (Fig. 50) will help to make the following
description of the process intelligible.
Holes were first bored as shown by the strong black lines,
and cleared to at least i metre below the lowest level of the
foundations. Cement grout was then poured into each bore,
and the pouring continued until the grout filled the bore to the
level of the roadway or pier tops. When the bore was full, the
pressure exerted by the column of cement at the bottom of
the bore was, in the case of the bores made from roadway level,
26 tons per square metre (2'4 tons per square foot), and, in the
case of the two others, 19 tons per square metre (1*76 tons per
square foot). So great a pressure was sufficient to force the
cement into all cavities in communication with the bore, so
that the grout must first have enveloped all loose material, and
then, by its property of setting, have compacted it into a solid
mass. That the cement did not fail to set was sufficiently
proved, as in several instances it was brought up in a hard
state when clearing the adjacent bore to which it had travelled
below the floor.
METHODS OF CONSTRUCTION.
IfeS
In consequence of the success obtained at the Delta barrage,
cement grout was employed to overcome difficulties of construc-
tion in other troublesome works which the irrigation officers of
Egypt had to execute. One of these it may be of advantage to
instance as affording an example of the combination of the two
DELTA BARRAGE
BORES FOR GROUTING
CROSS SECTION
^
1 1
/K
1 1
6
i
K
■
IS .
FIQ 60
PLAN
A
B
l^OWAV OVER BARRAi
RRAAC
^
systems of well-sinking and cement grouting for getting in
foundations below water level. Reference has already been
made to the Ismailia Canal head when describing an arrange-
ment for making a water-tight closure in the intervals between
wells. On account of the treacherous nature of the subsoil
which would have to bear the weight of the work, it was
decided to sink wells below the general floor foundation level,
l66 IRRIGATION.
with the object of giving increased support to the lock and
abutment walls and of providing curtain walls up stream
and down stream. By the addition of a few wehs elsewhere a
continuous boundary of wells was formed enclosing the whole
foundation area. These were sunk to the required depth, their
tops being then at about the level of the future floor surface. To
execute the well-sinking, as well as the necessary preliminary
excavations, a bank had to be formed on the Nile side to keep
out the river water, and pumps had to be constantly at work to
keep the inside water down. The excavation of the foundation
pit was carried down by hand as low as possible, which was to a
level some 2 metres (6 feet) short of floor foundation level. As at
this level strong springs rose over the whole area of the founda-
tions through black sand in a formidable manner, and as
previous experience had shown how difficult it was to build
sound work on such a substratum of quicksand with springs
rising through it everywhere, it was decided to get in the floor
platform all over the area bounded by the wells by the cement-
grouting method, as was done in the construction of the weir locks
of the Delta barrage. The programme which was followed was
this : After closing the intervals between the wells by iron piles,
the "saddle-back " and rubble pitching up stream of the regulator
and lock were completed to the extent shown in Fig. 46. The
wing walls were built up over their wells to a considerable
height above the finished level of the floor. The river dam was
then cut, and the water allowed to rise in the pit and find its
own level. A sand dredger was next admitted through the
opening in the dam, and the foundations of the floor were
dredged out to full depth. The dredger having done its work
made its exit, and the cut in the dam was closed again. The
grouting pipes and staging were then arranged over the founda-
tion area. As soon as the pipes were in place rubble was
thrown in round them to the required height of nearly 2 metres
(about 6 feet). Grouting was then carried on after the manner
already described, and continued till the floor rubble was grouted
METHODS OF CONSTRUCTION. iby
to the top. The work was left undisturbed for three days, after
which the pumps were set to work to lower the water in the
enclosed foundation pit. When the surface of the grouted
platform had been laid dry and cleaned, it was found that the
operation had been successful, and that there were no springs
left to interfere with the work. The floor was then completed
and the superstructure built in the dry.
It is sometimes desired to lay a syphon under a running
canal which cannot be closed for a period sufficiently long to
allow of its construction in the ordinary manner. The usual
method would be to divert the canal into a temporary channel
passing outside the syphon site. But there are some situations
where a diversion cannot be made except at a prohibitive cost.
In such cases some method of laying the syphon under water
must be devised. In Egypt several pipe syphons of 5 feet
diameter, some of them over 250 feet in length, have been laid
in running canals without resorting to the usual method of a
diversion. The barrel of the syphon may consist of a pipe of five-
sixteenths to half an inch thickness of mild steel plate, stiffened
with angle irons and cover plates. The pipe is put together on
the canal bank in the neighbourhood of the syphon site. The two
ends of the pipe are closed with water-tight doors, and means of
admitting water provided. The pipe is then launched and
floated into correct position over a trench which has been
dredged out across the canal ready to receive it. Temporary
banks, made round the outer ends of the dredged trench, connect
the extremities of the canal banks which have been cut through
to form the trench for the pipe. The pipe is now ready for
sinking. It is dangerous to let the water into it and leave it
to find its own way to the bottom. It would certainly tilt in
doing so, one end sinking and the other rising up out of the
water, and the joints would be so strained that a leak would
probably be the result. To control the sinking, the pipe should
be supported at both ends by ropes manipulated from rafts or
boats, and the ropes should be paid out evenly, so that the pipe
1 68 IRRIGATION.
may be let down quietly in a horizontal position on to its bed.
When the pipe is in place, the canal banks are remade over it
in their former alignment, and the ends of the syphon outside
the canal banks completed.
The building of the masonry ends, or the fixing on of the
rising terminal pipes, is sometimes a matter of considerable
difficulty on account of the proximity of the flowing canal. In
the case of a syphon of two pipes of 5 feet diameter laid, by the
system just described, under the Ibrahimia Canal, in Upper
Egypt, the ends were formed of bent continuations of the
horizontal pipes rising to the inlet and outlet levels at either
end. After the horizontal lengths had been successfully got
into position and the canal banks remade over them, it was
found impossible to get rid of the water about the pipe ends so
as to admit of the rising lengths being added. So the horizontal
lengths were lifted again, the bends and part of the rising ends
added above water, and the sinking irepeated. In this way the
work was successfully completed.
The same difficulty of building the ends of another syphon
in Egypt was surmounted in quite a different way. The syphon
was a simple pipe of 5 feet diameter with masonry inlet and
outlet wells at its extremities. The pipe was got into place
successfully, but the endeavour to complete it by building
the masonry ends outside the banks was for a long time
abortive, on account of the high level water in the canal
close alongside and the moving sand below. Eventually a
masonry well was sunk as near the end of the pipe as
possible (Fig. 51), but there remained an interval of 6 to 8
inches between t4ie two. The pipe end was closed by a
wooden door and tarred canvas, kept pressed against the pipe
by wedges driven by divers between door and well. A crater
was then dredged out with its bottom from 18 inches to 2 feet
below the under-side of the pipe. An upright grouting pipe,
perforated at its lower end, was fixed as shown in Fig. 51.
Rubble was then deposited at the bottom of the crater up to a
METHODS OF CONSTRUCTION.
169
third of the pipe's diameter, and the mass grouted up. A box
was then formed on the top of the grouted block with the well-
face as one side of it, and the box was filled with rubble to a
height of 2 feet over the pipe. The contents of the box were
then grouted up to the top. After a couple of days the water
in the well was pumped out, and a passage cut between the
well and pipe to the same diameter as the pipe and in prolonga-
tion of it. The collar of grouted rubble was found to have
formed a perfectly water-tight joint between the well and the
pipe. Both ends of the syphon were treated in the same way.
END OF PIPE-SYPHOM
FIG 6t
The well walls were then cut down on the outside to the proper
levels for the sills, and the slope revetments completed.
The tunnel which was designed to carry a double line of rail-
way under the Detro/t river, between Windsor on the Canadian
side and Detroit on the United States side, was constructed on
somewhat the same system as the S5rphon just described. The
tubes were floated into place and sunk into a trench dredged
out to receive them. But the tunnel was made up of several
tube lengths which had to be fastened together under water.
The manner of caulking the joints between two adjacent lengths
was thus described in the Standard of November ist, 1906. The
170 IRRIGATION.
passage is quoted here as the device may be found useful in the
construction of irrigation syphons. " Each tube when manu-
factured will be fitted with a sleeve at one end, which can slip
over the end of the adjoining tube previously sunk. The sleeve
is to be provided with a flange which can be bolted to a coi re-
sponding flange of the adjoining tube, a rubber gasket being
placed between the two. A similar rubber gasket is to be pro-
vided at the inner end of the sleeve, bearing up against the edge
of the next tube. In bolting up the flanges, which must be
done by divers, the rubber gaskets must be squeezed together
between the ends of the tubes to form a tight joint. This space
will be filled with a grout of pure cement. The ends of the
tubes at the joints are, further, to be fitted with flange angles
on the inside for the purpose of caulking between them should
the joints be found to leak. In order to enable the contractors
to begin lining the tubes before the sections are sunk all the
way across the river, some of the tubes may be provided with
bulkheads to keep out the water when the tubes laid are being
pumped out ."
The work was begun in 1906 and finished in 1910. It will
be found described in a paper by W. J. Wilgus, No. 3915,
Detroit River Tunnel : Minutes of Proceedings of the Institution
of Civil Engineers, 1911.
CHAPTER VIII..
MEANS OF DISTRIBUTION.
Canals and Drains.
In Chapter VI. the means of drawing water from the source
of supply were considered. In this chapter a description will
be given of the means by which the water is carried from the
source and distributed to the fields on which artificially irrigated
crops are to be raised.
A canal system consists of channels to carry the water, of
regulating works (usually of masonry) to control its flow, and
of drains to discharge surplus water from the irrigation zone.
The irrigation channels are usually classified under the heads
of main canals, branch canals, distributaries, and field channels.
Assuming that the position of the offtake has been selected,
the main canal, between its head and the point where it first
enters the tract to be irrigated, should be carried along the
alignment which is economically the most advantageous. The
shorter this unprofitable length of canal can be made the
better, provided that the selection of a favourable site for the
head works is not unduly influenced by the claims of economy
to the neglect of more important considerations. Within the
area commanded — that is, inside the limits of the land which
is to be brought under irrigation — the alignment of the canals
must be such as to facilitate direct irrigation from them. It
the country is made up of ridges and intervening depressions,
the main canal should run along the principal ridge. Its
branch canals should follow the subsidiary ridges, and the
distributaries the minor ridges, so as always to keep the water
at a height which will command the land to be irrigated and
172 IRRIGATION.
in a position to flow on to the fields, and also to avoid crossing
the natural drainage lines of the country. If a contoured map
exists, it is more or less a simple matter to lay down upon it
the scheme of canals and drains adapted to the natural con-
figuration of the ground. But the configuration may not be
one of alternating ridges and depressions. There is need
sometimes of designing irrigation systems to serve the flat
lands which are found bordering a river that flows along a
valley. If the river follows the lowest line of the valley bed,
these plains have a surface slope towards it ; but if the river
occupies a broad valley and has raised the land level alongside
it by the deposit of successive floods, the land surface slope
falls away from the river, as with the Nile valley in Upper
Egypt. In the former case the canal would be aligned along
the outer edge of the flat tract at the foot of the rising ground
enclosing the valley, and in the latter case along the high
margin adjoining the river. The flat lands {vegas) of Anda-
lucia, in Spain, bordering the river Guadalquivir, may be
taken as an example of lands sloping towards the river. A
canal to irrigate them would have to be aligned along the foot
of the hills that bound the valley, and would unavoidably cross
cJl the drainage lines leading to the river. At every crossing
a passage for the drainage water would have to be provided.
But, whatever may be the nature of the country through
which canals are carried, no attempt must be made to prevent
the drainage from flowing along the line to which it has
established a "right of way," if provision can be made for
its unimpeded passage by constructing either a syphon to
carry it under the canal at the point of crossing, or some
other work serving the same end. It may, however, in some
cases, be preferable to divert the drainage and carry it away
in a new channel made expressly for it. But, in any case,
the universal rule applies that the drainage must not be
ignored, and full provision must be made for the disposal of
all excess water, whether it be due to rainfall or irrigation.
MEANS OF DISTRIBUTION. I73
The principles that govern the alignment of drains are the
converse of those applicable to canals. If natural drainage
channels do not already exist where drainage is a necessity,
artificial drains must be aligned along the lowest lying land,
that is, along the bottom of the depressions or valleys between
the ridges on which the canals and distributaries run.
The next things to consider are the points which influence
the design as regards the longitudinal section of the irrigation
and drainage channels. The most important matter affecting
the question of the gradient of main canals is silt deposit.
Silt is the eroded matter which is brought down in suspension
by rivers from their upper reaches. The greater the velocity the
more and the heavier is the silt that the water carries along
with it. When the river leaves the hills and ceases to be
torrential, it drops its heaviest loads of shingle and boulders,
but keeps the sand and soft mud for distribution in the plains.
Before the river nears the sea it has left behind all but the
finest sand and mud which give the richest deposit of all.
There is silt which is fertilising, and there is silt which is sterile.
The former it is desirable to draw into the canals and carry
forward to the fields in abundance ; the latter it is better to
exclude from the canals altogether, if possible, as being so
much "dead weight in the boat." At the same time, it is
important that the deposit of silt in the canal itself should be
a minimum. As silt deposit takes place wherever there is a
change of velocity from a higher to a lower rate, the velocity
of flow in the canal which ensures the transport of a maximum
amount of silt to the fields with a minimum of deposit on the
way, should theoretically be the same as that of the river at the
point where the canal takes off from it. j^ But it is rarely, if
ever, possible to carry this theory into practice, for not only
does the river velocity vary at diiTerent seasons, but it is
sometimes so high that, if the canal were to flow at the same
rate, its water surface slope would be steeper than the slope
of the country, and the water would never come to land
174 IRRIGATION.
surface. Consequently it is found more practicable to make
the rate of river-flow past the offtake approximate to that
of the canal than to make the canal agree with the river.
This is brought about by working the gates of the under-
sluices in the river weir or regulator, and the shutters of the
canal head, in such a way as to discourage as far as possible
strong currents and eddies in the neighbourhood of the head
sluice, and to produce comparatively still water at the canal
offtake. The coarser and heavier silt is carried along by the
lower water in contact with the bed of the river, and it is
this material that it is desirable to exclude from the canal,
for these two reasons, namely, that, if admitted, it is sure to
cause troublesome deposit in the first reaches of the canal ;
and, even supposing some of it succeeded in reaching the
fields, it would not be welcomed there, for it would have taken
the place of the lighter and more fertilising silt which is so
valuable to farmers. To prevent the admission of this heavy
and infertile matter, it is necessary to draw in the upper water
from the river and to exclude the lower. This is sometimes
effected by giving the canal a head sluice of considerable
length and a raised sill, and by working the shutters in such
a way that the top layer only of the river water may be drawn
into the canal. But this method of drawing off from the river,
and of reducing the rate of flow past the canal head by closing
the adjacent under-sluices, will cause some of the excluded
silt to be deposited in front of the head sluice and above the
under-sluices. This must be got rid of by periodically opening
the under-sluices, so as to create a sufficiently high velocity to
scour away the deposit. While this operation is being carried
out, the canal head should be temporarily closed. In this way,
by an intelligent management of the regulating gates of the
under-sluices and of the canal head, the silt difficulty, which
has troubled every irrigation engineer, may be at least partially
overcome. The head sluice must therefore be so designed that
water may be admitted to the canal in accordance with these
MEANS OF DISTRIBUTION. 175
principles, which have been deduced from the teachings of
experience, chiefly in India (Buckley, Chapter III.).
It is not, then, the river velocity that determines the velocity
of flow that is to be adopted for the canal, but other considera-
tions. If the canal is to be navigable, it is desirable that the
velocity should be as low as is consistent with its more
important duty of irrigation, the avoidance of silt deposit, and
a reasonable regard for economy The lower the velocity of
flow the larger the cross-section must be to carry the required
discharge, and consequently the greater the cost of making the
canal. If the velocity is too low, silt deposits in the canal,
the discharging capacity of the canal is diminished, and much
expense is incurred in clearing out the deposit. If the velocity
is too great, the reverse takes place ; the bed is scoured out, the
banks are undermined and slide forward, and the channel soon
becomes irregular. Neglecting the needs of navigation, the
ideal velocity is that which will neither create scour nor
encourage deposit, but will enable the water to carry forward
the silt which comes into the canal from the river, and keep it
in suspension until the field, which is to be irrigated, is Anally
reached. There both the water and its silt will find useful
work to do. What this ideal velocity should be varies with
the quality and quantity of the silt that the river carries in
suspension, and with the nature of the soil forming the bed
and banks of the canal.
In India Mr. R. G. Kennedy has attempted to determine this
point. He selected for his observations certain canals in which
the flowing water carried a constant percentage of silt in
suspension. The cross-sections and velocities at thirty sites,
where no silting or scouring took place, were measured, and it
was found that at all these sites the following equation
expressed very approximately the invariable relation between
the mean velocity and the depth of the water : —
\ = cdr = 0-84 d-'^
Thus the higher the velocity the greater would be the correct
176 IRRIGATION.
depth, and vice versa. Therefore it follows that, for a given
discharge, canals with a high velocity should be comparatively
narrow and deep, and those with a low velocity wide and
shallow. On different canal systems the values of c and m in
the above formula might be expected to vary slightly. It
would appear that Mr. Kennedy's conclusions require further
testing before they can be confidently accepted as the expression
of prevailing law.^
It is chiefly the flood conditions that have to be taken into
account in determining the figure to adopt for the velocity of
flow in the canal. During the season of low discharge the
river carries little or no silt ; in flood it is carrying its maximum.
In Indian rivers during flood, the proportion by weight of solid
matter to liquid may be as great as i to 30. It frequently
happens that the conditions are such that silt is deposited in
the canals during flood, and picked up and carried away by the
clearer water that enters after flood, even though the velocity
in the latter case may be lower. This is due to the fact that,
in flood, the water admitted brings in more silt firom the river
than the canal velocity enables the water to keep in suspension ;
whereas, after the flood, the clearer water is not Ccirrying all it
can, and so picks up some of the lighter silt as it goes along.
Mr. Buckley instances the case of the ^irhind Canal in India,
on which careful observations of silt deposit have been made.
In August and September the velocities observed were 3*2 and
3*6 feet per second respectively, and with these velocities silt
was deposited : in October and November the velocities were
3*5 and 3"3 feet, and the quantity of silt that was removed in
these two months was more than double the quantity that
had been deposited in the two preceding months. In the
two later months, when scouring replaced deposition of silt,
the velocity of current was only slightly increased, but the
flowing water was clearer. From experiments made during
the flood season in Lower Egypt, Sir William Willcocks came
to the conclusion that, in canals with their heads suitably
*■ See Note 8, Appendix IV.
Means of distribution. i?7
placed, a mean velocity of from 70 to 100 metre (2*30 to 3'28
feet) per second is sufficient to prevent any appreciable deposit,
but that deposit takes place with mean velocities of '60 metre
(2 feet) a second and under. In Lower Egypt the silt carried
by the river is very fine.
It may be stated, as a conclusion based on experience in
India and Egypt, that a velocity of from 2 to 3 feet a second is
required to carry forward ordinary silt, the required velocity
being greater or less according as the matter in suspension is
coarse or fine, and the water heavily or lightly charged with
silt.
The velocity of flow depends on the surface slope of the
water in the canal. In the first reach of the main canal,
between its head and the upper limit of the land commanded
by the canal water, the water surface slope must be steep
enough to produce a velocity that will decidedly discourage silt
deposit. But, provided this condition is fulfilled, it is advan-
tageous to have a surface slope of low gradient, as the flatter
the slope is, the shorter will be the length of canal required to
bring the water to country surface. Within the commanded
area the surface slope of the canal is determined, in most
cases, by the slope of the land. If, however, the land surface
is so steep that a water surface slope which conforms to it
gives an inconveniently high velocity in the canal, the canal
must be divided up into reaches with a suitable gradient,
produced by impounding the water at regulating falls situated
at the lower end of each reach.
The velocity of flow and water surface slope having been
determined from the foregoing considerations, there remains to
be calculated the discharge the canals will have to carry. The
data for this calculation are the area of crop to be irrigated
and the accepted " duty " of water for the period of maximum
demand. In India the kharif season and in Egypt the
flood season are the periods in which the canals have, in most
cases, to carry the greatest discharges. Mr. Buckley states
L K
178 IRRIGATION.
that, " as a general rule, main canals irrigating khareef (or
monsoon) crops should be capable of carrying a maximum
discharge of i cubic foot per second for every fifty acres of that
crop which it is intended to irrigate, and they should be capable
of carrying i cubic foot for each 100 acres of rabi (cold weather)
crops. The extent of land which can be irrigated may be
determined either by the quantity of water available in the
source of supply or, when the quantity is abundant, by the
area which can be commanded by the system."
In Egypt, during the Nile flood, the supply is abundant
and sufficient for the area commanded. The whole of
the perennially irrigated tracts are commanded by the canal
systems of Egypt, and so the area commanded becomes
identical with the gross area. The discharge which the
canals have to carry in flood to serve this area is calculated
at the rate of 25 cubic metres a day per acre. This is equivalent
to an allowance of i cubic foot a second for every ninety-eight
acres. The area under rice in Egypt is insignificant as compared
with the total area under irrigation during the flood season ;
othervnse it would have to be separately allowed for in the
estimate at double the general rate. Nevertheless it is as well to
add a small percentage to the total to provide for the rice crop,
and also for the washing of salted lands which is carried on when
water is plentiful. The allowance in Egypt may therefore be
taken to be rather more than the rabi allowance of India of i
cubic foot a second for every 100 acres.
The velocity of flow and the maximum discharge are the
factors with which the calculations of the dimensions of a
canal are made. ' Its cross-section must come under considera-
tion at this stage. A theoretically perfect cross-section for
a large canal demands a depth that would be found unsuitable
for several reasons. Not only would the original excavation of
the canal in deep cutting be difficult and costly, but the sub-
sequent maintenance of a clear channel to full depth by
dredging or otherwise would be troublesome. It can be readily
MEANS OF DISTRIBUTION. 1 79
understood that the cost and difficulty of excavation becomes
very great as soon as spring level is reached. The depth of
large canals is, therefore, made as great as may be found con-
venient under the conditions affecting the question. The width
that will give a channel of the required discharging capacity is
then found by the help of hydrauHc tables.'
As examples of the head reaches of canals in cutting, two
sections are given (Fig. 52). The upper one is typical of Indian
canals ; the lower is that of a recently made canal in Egypt.
In India, where rain falls heavily, it is necessary to make a
Si
MAIN CANALS \N CUTTING
TYPICAL SECTION ^Oj, ,.0. PIQ 62
SECTION
CANAL ABBAd
eGY(*T
system of drains on the inside berms to prevent the slopes
being worn into gutters. In Egypt the rainfall is so light that
this precaution is unnecessary.
Main canals are run with a constant supply, and with a water
surface not necessarily above country level. It is, in fact,
desirable to keep the water level as low as possible, consistently
with a delivery at convenient levels to branch canals, for
several reasons. Direct irrigation from a main canal should
be discouraged as much as possible on account of the difficulty
of effecting a fair distribution of a limited supply of water by
' Jackson> " Canal and Culvert Tables," Higham's " Hydraulic Tables,"
aiid Colonel Moore's " New Tables," will be found useful. See Appendix II.
N a
l80 TRRIGATION.
any system of rotations when such a practice is allowed. More-
over, as main canals flow with a water surface at a constant
level for long periods, it is best to keep the water within soil to
avoid the evils of infiltration and consequent vraterlogging
of the soil outside the canal. To provide for the irriga-
tion of the land adjoining a main canal, parallel high level
distributaries should run alongside to take up the direct
irrigation.
It is not possible to define in terms that are universally
applicable a main canal, a branch canal, and a distributary.
It is not always easy to decide where a main canal becomes a
branch canal, or where a branch canal becomes a distributary.
A branch canal is at any rate intermediate in position and
partakes of the nature of the other two. To design branch
canals and distributaries correctly it is necessary first to con-
sider what will be the future methods of water distribution.
According to the practice common to almost all countries in
which irrigation is established, the distribution of water is
effected, at any rate during seasons of short supply, by some
system of rotation. Under such a system water is alternately
supplied and withheld for certain fixed periods, so that each
distributing channel flows only for the time required to irrigate
the crop depending on it, and not during the intervals between
waterings. This method of distribution will be fuUy described
in Chapter X., but it is necessary to refer to it here, as the
design of the distributaries has to be based on the method to
be adopted. Suppose, for instance, that the rotation pro-
gramme arranges that water shall be supplied for seven days
and be cut off for the following seven. The discharge, which
has been calculated on the basis of a continuous flow, must,
under such a supposition, be doubled, as it will have to do the
same amount of work in half-time. The distributaries of the
Ganges Canal in India, as originally designed, did not contem-
plate any distribution by rotation. Many of them have, in
consequence, been lately remodelled so as to enable them to
MEANS OF DISTRIBUTION. I8l
run every alternate week instead of continuously as they
formerly did.
In Egypt, for summer irrigation, the distributaries of each
separate system are divided into three groups, to each of which
water is given in succession for a third of the whole period of
rotation, or interval between waterings. Therefore, as the
irrigation has to be effected in a third of the time that would be
taken by a constant discharge, the distributary must be capable
of carrying three times the discharge calculated on the basis of
a continuous flow. It has been shown in Chapter III. that 12
cubic metres a day per acre commanded is the continuous
discharge required to irrigate the summer crops of Egypt,
assuming a watering every eighteen days. This being the
allowance for a continuous flow, the discharge required to
complete the irrigation in a third of the time, or six days, must
be calculated at the rate of 36 cubic metres a day per acre
commanded below the point that is being considered.
On the Sone canals in India closures of entire distributaries
for half-time were provided for, and the channels were designed
to carry twice the volume which would have been allowed
with a continuous flow discharge. Mr. Buckley considers
this period of closure excessive, and is of opinion that
five days' closure in fifteen is sufficient. Agreement between
Indian and Egyptian practice is not to be expected. Irrigation
problems in India are more complicated than in Egypt on
account of the greater variety and complexity of the condi-
tions. In Egypt, rainfall, being a negligible factor, introduces
no compHcations. The fact also that practically all cultivable
land in Egypt is irrigated, so that the area commanded and
the total area under cultivation are the same, simplifies many
questions of irrigation. That is why Egypt furnishes so many
useful illustrations of irrigation principles, the varying factors
of other countries being eliminated.
The best form of distributary channel is found by Neville's
rule in this way: " Describe any circle on the drawing board;
1 82 IRRIGATION.
draw the diameter and produce it on both sides ; draw a tan-
gent to the lower circumference parallel to this diameter, and
then draw side slopes at the given inclinations, touching the
circumference on each side and terminating in the parallel
lines. , The trapezoid thus formed will be the best form of
channel, and the width at the surface will be equal to the sum
of the two side slopes." The usual value to give to the side
slopes of distributaries is i to i. An ideal section, including
the banks, is given in Fig. 53
Distributaries should be so designed, as regards their longi-
tudinal section, that the lands served by them may be readily
irrigated free-flow. This principle has been opposed at different
CROSS SECTION OF AN
IDEAL DISTRIBUTARY
PIG 53
8-A-6- *-— -14,- — )(i-6-»-T--%-»-9if-6-*— 8— ^
r^
W.L., ! \^y'^^^^S—<^ C.L.
times by those who have maintained that lift irrigation is
the healthy system, and flush irrigation the reverse. Water-
logging of the soil and salt efflorescence have resulted from the
long-continued maintenance of canal water levels above country
surface. The remedy for these evil effects of infiltration was
held to be a permanent lowering of the canal water levels, and
a resort to lift irrigation. But neither India nor Egypt has
accepted this view. The advantages of flow irrigation are as
obvious as the ill effects of infiltration. The system to be
preferred is one that will avoid the ill effects without losing
the advantages. The first condition for a healthy system is
effective drainage at all times. When that has been secured,
no harm will come of high levels in the canals, provided they
are produced for short periods alternating with equal or longer
periods of low levels. With these provisoes an easy, cheap, and
MEANS OF DISTRIBUTION. Ib3
plentiful water supply is an unmixed blessing to agriculture.
A liberal supply of water, combined with a perfect system of
drainage, will provide the means for washing salt out of the
soil that is impregnated with it, if the water is delivered free-
flow. It would be useless to attempt such washings where
water has to be lifted, as it would not pay. To prevent any
harmful effect from infiltration due to high levels, the canals
should be run at high and low levels alternately. The system
of irrigation by rotation lends itself to this arrangement. Such
an alternating or intermittent supply keeps the water in the
soil from stagnating, gives free-flow during the high level
period, and affords relief to the drains during the low periods
by reducing the excess resulting from wasteful irrigation. The
canals also themselves, when low, act as drains to those lands
alongside them which have imbibed too freely during the high
level period.
There is another reason for designing the distributing canals
so that they may deliver their water free-flow. During the
floods of certain rivers the water carries along with it rich
fertilising matter, brought down from the hills or catchment
basins where the rains which cause the floods fall. It is most
desirable to secure on the fields as much of this silt as possible.
Therefore, during flood, the canals should be run with liberal
supplies, and at such levels that the water can be readily made
use of. But there must be limits to this liberality, as, other-
wise, either the drains will have to be made extravagantly
large, or they will be called upon to do more work than they
can efficiently perform. The alternation of weeks of high
level and of reduced supply — not necessarily low supply —
seems to afford the most convenient compromise that g^ives
the advantage of a sufficiently liberal supply without the
detracting accompaniment of bad drainage.
The distributaries, therefore, must be designed to give free-
flow irrigation when running full supply. Under the rotation
system they irrigate only when at full supply. A suitable full
1 84 IRRIGATION.
supply level for the water of a distributary will then be repre-
sented by a line approximately parallel to the land surface and
about a foot above it.
Those branch canals which perform the duty of direct
irrigation should be designed as if they were distributaries;
while those that act in the same way as main canals, that is,
merely as carriers of water to the heads of the distributing
channels, should be reckoned main canals.
The application of the foregoing principles may be illustrated
by taking the case of the distributing canals of the delta of
Egypt. During the period of short supply in summer a three-
section rotation is applied ; that is, each of the three sections
into which separate canal systems are divided has water for a
third of a rotation period (or interval between successive
waterings), and is without it for two-thirds. If the full period
is fixed at eighteen days, each section gets water for six days
and is without it for twelve. As has been already shown, the
distributing canals must carry during their supply period a
discharge calculated at the rate of 36 cubic metres per day per
acre commanded. During the flood season the programme is
altered. The distributing canals are given full and reduced
supply in alternate weeks. The allowance in flood is at the
rate of 25 cubic metres per day of continuous flow per acre
commanded. « If the flood rotation programme provided for the
whole volume being delivered in one half-period, and nothing in
the other half -period, the channels would have to carry 50 cubic
metres per day per acre for half-time. As this figure is greater
than the summer discharge of 36 cubic metres, this larger flood
discharge would determine the dimensions of the canals.
But it has been found undesirable to reduce the discharge to
nothing in one half-period, and better for the general conve-
nience to arrange that the discharge of the low period may be
about half the discharge of the high period. Thus the high
period discharge would be at the rate of 33 cubic metres, and
the low period discharge at the rate of 17 cubic metres, per day
MEANS OF DISTRIBUTION. l8S
per acre. As, however, the summer programme requires that
the canals shall be able to carry a discharge at the rate of
36 cubic metres per day per acre, this figure, being the larger,
determines the dimensions of the canals, and represents full
supply. The distributing canals during the flood would then
run full supply one week, and at reduced supply, or at the rate
of (50 — 36 =) 14 cubic metres per day per acre, the alternate
week.
Summing up the results obtained in the particular illustra-
tion chosen, the main canals (and branch canals serving as
carriers onlj') would be designed to carry a continuous dis-
charge calculated at the rate of 25 cubic metres a day per acre
commanded ; the distributaries (and branch canals acting as
distributing channels) would be designed to carry a maximum
discharge calculated at the rate of 36 cubic metres a day per
acre commanded. The flow of the latter in summer would be
intermittent, the water being cut off for periods equal to double
the duration of the periods of supply. In the flood season the
canals would flow alternately at full and half-supply for equal
periods.
This example is no more than an illustration of the appli-
cation of principles to a particular case. Every country will
have its own peculiar conditions which will determine how
the principles of design should be adapted to its convenience
and advantage.
A scheme of drains should form part of the original project
for the irrigation of any tract of country that includes low-
lying lands. But it can scarcely be said that this rule has been
followed in the past in those countries where irrigation has
been practised. The history of irrigation shows rather that
canals have first been made and used for a long time before
any attention has been paid to drainage. It was assumed that
it could take care of itself, and that rainfall and the surplus
water of irrigation would disappear somehow by evaporation,
1 86 IRRIGATION.
absorption, or otherwise. To some extent, in high-lying lands,
drainage will take care of itself provided the natural drainage
channels are not interfered with. But in low-lying lands the
evils that result from neglect of drainage will inevitably call
attention to the subject. The postponement of its considera-
tion until after the canals .have been made is now recognised as
wrong in principle. This does not mean that a complete
system of drains should be laid down at the time of the
carrying out of an irrigation project. But the main drains and
branches, and all drains in fact which it is certain will be
necessary, should be; included in the scheme. The necessity
for additional drains will doubtless arise as the irrigation
develops, but they can be made when the want of them is felt.
The history of the construction of the Ganges Canal in India
and its subsequent remodelling to provide for drainage, which
had been disregarded in the first instance, forms an instructive
lesson for irrigation engineers. In Egypt twenty years ago
there were no drains, and much land had been ruined for want
of them, and more was in process of being ruined. Since then
hundreds of miles of drains have been dug, and not only is
the further spread of the evil stopped, but the lands that were
ruined are being reclaimed to cultivation. In the west of the
United States the same mistake was made as had been made
before in Egypt: natural drainage lines were converted into
irrigation channels, with the inevitable result of waterlogging
the soil and rendering it uncultivable. The San Joaquin
valley in California has suffered from this injurious practice.
Most countries, in short, which have occupied themselves with
irrigation, have learnt sooner, or later that drainage also must
receive its due share of attention.
A drain to be efficient must be designed with a waterway
of such levels and dimensions that it will carry away the
surplus water of the area served by it, with a water surface
always well within soil. The water level in the drain should,
if possible, be kept at least 3 feet below land surface. The
MEANS OF DISTRIBUTION. I87
maximum discharge which should be provided for will be pro-
portional to the area to be drained, and will depend on the
rainfall as well as on the description of irrigation practised.
Land under rice crops discharges at least double the amount
that land under ordinary crops does. If the rainfall is con-
siderable it is probable that land depressions will be well
marked and be traversed by natural drainage lines which may
take the place of the main drains of an artificial system. But, if
that is not the case, the main drains, as well as subsidiary
drains, must have sufficient discharging capacity to carry away
both rainfall and excess canal water. It is, of course, impossible
to lay down what allowance must be made for rainfall when the
conditions are not known. The amount of rainfall, its intensity
for short periods, the season, the soil, the configuration of the
ground, all affect the question, and must be taken into account
when the drainage scheme is being elaborated.
Neglecting the question of rainfall, it is possible to state the
principles on which the drains should be designed to enable
them to carry off the surplus water resulting from irrigatioa.
A system of drains is the converse of the system of canals with
which it is associated. The main drain, which forms the tail
of the drainage system, corresponds with the main canal that
forms the head of the irrigation system ; the subsidiary drains
correspond to the distributing irrigation channels. As the
main canal carries water to the channels which distribute it, so
the main drain carries away the water which the subsidiary
drains collect and discharge into it. The discharge of the
main drains will be more or less constant for prolonged periods,
as the total drainage of a large extent of country is, on the
average, the same throughout a season. In correspondence
with the irrigation periods of rotation, the flow in branch drains
will be intermittent. Some will be discharging at one time
and some at another, so that those that are discharging are
balanced by those that have ceased to discharge, and the
aggregate discharge of all the collecting drains of a system
1 88 IRRIGATION.
becomes a fairly constant quantity. H^nce the dimensions of
the main drain should be calculated on the basis of a con-
tinuous flow. The question is, what discharge per acre of land
served by the drain must be allowed in order to arrive at the
amount of run-off. The maximum discharge to be admitted
into the canal system for the purpose of irrigation will have
been previously determined as the basis on which the canals
were designed. The maximum discharge in any drain should
naturally be something less than the maximum admitted into
the canals. For a main drain, below the inflow of the lowest
branch drain, it would probably be sufficient to provide for a
third of the irrigation maximum. This allowance would
contemplate a continuous flow. But on the branch drains the
discharge becomes more intermittent and fitful the higher in the
system the drain may be. For this reason the minor drains must
be allowed a comparatively large section, as they will have to
carry off the water as it reaches them, that is, in half time or
third time. In the case of the main drain a third of the irriga-
tion volume was assumed to run off, but in the case of the minor
branch drains at the upper extremity of the drained area it is
well to calculate that half the maximum irrigation allowance
per acre, used to determine the dimensions of the distribu-
taries, may have to be carried by the drain at some time
or other. The drains which are intermediate between the
uppermost branches and the main drain would be given sections
capable of discharging volumes calculated at a rate per acre
which would be less than that used for designing the minor
branch drains above them, but greater than that provided for
by the dimensions of the main drain.
As the delta of Egypt has furnished an illustration for
canal design, it will be useful to complete the example by
applying the foregoing principles to its drainage system. For
this purpose Egypt is the most favourable instance to select,
since, as has already been stated, its rainfall is negligible and the
whole area commanded is irrigated. The maximum discharge
MEANS OF DISTRIBUTION. 189
admitted into the main canals is at the rate of 25 cubic metres
a day per acre commanded. Therefore the main drain, which
should carry about a third as much, will be designed to dis-
charge at the rate of 8 cubic metres a day per acre served by it.
The distributing canals are designed to carry a maximum of
36 cubic metres a day per acre commanded. The minor branch
drains at the upper end of the drainage system, which should
carry half as much, will be designed to discharge at the rate of
18 cubic metres a day per acre served by them. The inter-
mediate drains, according to their position on the drainage
system to which they belong, should be made capable of
carrying 15, 12, and 10 cubic metres a day per acre.
Deep drains are preferable to shallow ones, as weeds grow
less readily in the former. Drain water, being clear, encourages
the growth of weeds, whereby the efficiency of drains is often
much diminished. A low rate of velocity is also favourable to
weed growth. It is therefore better to give depth of channel
in preference to width to the extent that is practicable, and
also to give a comparatively steep gradient to the drain so as
to secure a high velocity of flow. This latter is often impossible,
especially in main drains near their outfalls if the land which
they drain is flat. Depth of channel must then be relied
upon to discourage weed grovrth. In large systems the main-
tenance of the depth can only, as a rule, be arranged for by
dredging. To secure a sufficient depth and velocity of flow
for the continuous discharge of the main drain, it is necessary
to avoid giving the channel excessive dimensions. If the
discharging capacity of the drain is just sufiicient, but no
more than sufficient, so that it vnU carry away the drainage
water with a depth that vnll prevent weed growth, the
drain will maintain its efficiency for a longer period than
it would do if it were of larger section and flowed with
less depth.
CHAPTER IX.
MASONRY WORKS ON IRRIGATION CANALS.
Masonry works are required on the distributing channels of
an irrigation system to give effective control over the supply
and its distribution. They may be classified as follows : —
(i) Regulating works to distribute the water and control its
levels, such as head sluices, regulators, escapes, and culverts ;
(2) Works to overcome an abrupt and decided change
of level in the canal system, such as falls and rapids or
cascades ;
(3) Works to provide for crossing drainage lines, such as
aqueducts and syphons;
(4) Road bridges at traffic crossings.
The head sluice of a canal controls its supply. In the
preceding chapter it was pointed out that, to meet the silt diffi-
culty, the head sluice of a main canal fed from a muddy rivei:
should be given a considerable length and a raised sill, and that
the shutters should be worked in such a way as to admit only
the upper water. Mr. Buckley, who was an advocate of these
principles and, as chief engineer of Bengal, a practical demon-
strator of their soundness, gives the following description of the
Trebeni Canal head sluice (Fig. 54) : —
"TheTrebeni Canal head sluice, which is now" (1905) "under
construction in Bengal, stands on the bank of the Gunduk river,
at a point where the flood rises over 20 feet. The sluice is
designed to give the required discharge with a depth of 2 feet
of water flowing over the tops of hurries or horizontal baulks.
The vents A A have draw-gates, worked by a screw and capstan
on the parapet. These vents will be used to some extent for
MASONRY WORKS ON IRRIGATION CANALS.
191
regulation, and will be closed entirely if the high floods carry
down heavy silt, which would be likely to choke the canal.
When the flood level is more than 2 feet above 969*50 the
supply will be drawn in over the top of the arch platform which
lies at that level. At that time the vents B B and C C will be
entirely closed. As the flood falls below the platform the
hurries in the vents B B will be removed, as required, and
the water will be drawn in over the top of them into the canal.
When the water level in the river falls to less than 2 feet above
the top of the platform at 961*00 the kurries in the vents C C
TREBENI CANAL HEAD SLUICE
Scale
10 6
lllllllllll
10
-tr
±
Feet
H.F.L
"vy
will be removed, as required, and the discharge will be regulated
over the tops of the kurries in those vents."
This is an excellent example of the application of the prin-
ciples on which a head sluice should be designed with the
object of excluding heavy silt from a canal." In this case there
is no raised sill, but the whole floor is 3 feet above the canal
bed level. There are twenty-two vents in this sluice, each
6 feet wide at A, 7 feet at B, and 7 feet 6 inches at C,
Vents of head sluices vary in width from 3 feet to 16 feet.
In Egypt the head sluices of the largest canals have vents of
5 metres (16 feet 5 inches) width. The waterway allowed is
determined by the discharge required and the available head at
192 TRRIGATION.
different seasons. It is a good rule to allow a liberal waterway
with a margin for meeting the demand for an increased dis-
charge which foture developments may create. The extra
allowance, beyond the area calculated to be necessary,
might conveniently amount to lo per cent, in large works and
25 to 30 per cent, in smaller works. The floor of a head sluice
and its up-stream and down-stream aprons will have to resist the
Scime forces and be subjected to the same action as a river
barrage, described in Chapter VI., and therefore should be
similar in design. Two large head sluices, lately built at
Assiout and Zifta, in Egypt, have been given practically the
same cross-section as the river barrages with which they are
associated. Head sluices, however, with narrower vents, and
at the head of branch canals, can be built of lighter construc-
tion than head sluices on a river, as the up-stream water level is
not subject to such great variation in a feeder canal as it is in
a river. The design of the superstructure depends to a great
extent on the description of regulating apparatus adopted, and
sometimes on the necessities of the traflic that will pass over
the sluice. The different forms of regulating apparatus will be
referred to later in this chapter.
In a general way the principles of design are the same for
all canal works of regulation which are subjected to a head of
water up stream and to scouring action down stream. The head
or the scour may be greater or less, necessitating a modifica-
tion of the design in those dimensions which are affected by the
one or the other. An escape or fall, as a rule, requires ample
protection down stream in the form of an extension of the floor,
well-revetted slopes, and a talus of heavy pitching, inasmuch
as a heavy discharge through it may continue to work under
an undiminished head for some time ; whereas in the case ol
a simple regulator, the canal below quickly fills up, and the
head is reduced. A basin regulator in a cross embankment
works under the conditions of an escape or fall, as it discharges
into an open basin requiring an enormous volume of water to
MASONRY WORKS ON IRRIGATION CANALS. I93
affect its surface level. It is therefore necessary to give the
same attention to the down-stream protection of basin regulators
as is required in the case of escapes.
Regulators are generally placed where a canal bifurcates, and
below the point where a branch canal takes off. They may
also be required across a canal immediately below an escape or
level crossing. They are, in fact, necessary or desirable wherever
a division of the water supply has to be made.
Escapes are the safety valves of a canal system. They
supply the means of disposing of any surplus discharge that has
to be got rid of, when, for instance, in consequence of a
slackening of the demand for water, the irrigating sluices are
suddenly shut down. This often occurs after a heavy fall of
rain without sufficient warning for the situation to be met by
decreasing the discharge entering the canal at its head. Escapes
are also useful in case of an accident to any of the canal works
requiring an immediate reduction of the discharge. They also
assist in producing a high enough velocity in the canal, when
it is carrying muddy flood water, to lessen silt deposit, and,
later on, when the water is clear and a surplus available, they
make it possible to maintain a high current in the canal whereby
silt deposits that have formed during flood are diminished by
scour. For these purposes escapes are most desirable on main
canals and long distributaries, not only at the tails, but at
intervals along their courses.
If possible, an escape should discharge into a river or well-
defined waterway, and not into a drainage line. This principle,
however, cannot always be carried out, and something short of
the ideal has to be accepted : a river may not be within reach,
and no well-defined waterways, other than drainage lines, may
offer themselves.
The design of an escape may be similar to that of a head
sluice, a regulator, or a fall, or a combination of them. But,
as already stated, the down-stream protection must be adequate.
An escape may take the form of a waste weir with a drop, and
I. o
194
IRRIGATION.
be protected down stream by a " rapid " or " cascade," the fall
of the water being divided between the drop of the weir and the
rapid forming its apron. On the crest of the drop-wall, shutters
or baulks or other regulating devices would, if necessary, control
the volume escaped.
Basin escapes which have to pass large quantities of watei
are sometimes formidable works. There is a fine work in
Egypt, of modern construction, known as the Kosheshah escape.
It was designed to discharge back into the Nile the contents of
a chain of inundation basins of an aggregate area of 555,000
KOSHESHAH ESCAPE
Scale
^1
t T y T y T fee> FIG 55
acres. It is capable of discharging 80,000 cubic feet a second
under a maximum head of nearly 15 feet. It has sixty uppet
vents and sixty lower ones of the dimensions shown in Fig. 55.
The lower vents are regulated by iron sluice-gates moved in
vertical grooves by an overhead winch. They are used to
admit water into the basins during the rise of the flood and
afterwards to assist in emptying them. The upper vents are
used only for the emptying. The latter are fitted with falling
gates hinged at their lower edges. A water cushion is provided
for the gates to fall upon by giving the upper floor a raised sill
of ashlar along its down-stream margin. The upper falling
gates can all be let go within a quarter of an hour if desired.
KOSHESHAH ESCAPE.
MASONRY WORKS ON IRRIGATION CANALS. 195
The object of providing for quick opening is to produce a wave
in the river after a poor flood so as to submerge certain high
islands and river-side lands which depend on the flood rise for
their irrigation but are of too high a level to be reached by
poor floods. The artificial wave created by the sudden empty-
ing of the basin contents back into the Nile has often succeeded
in eifecting the irrigation which the natural flood had failed to
complete. Plate VIII. gives a view of part of the Kosheshah
escape taken during construction but after the masonry had been
completed. The bottom gates were already in their grooves,
closing the lower vents, and an upper gate was being put in
place when the photograph was taken. In the bay to the left
of the one where the gate is being hung both the upper and
lower gates are in position, closing the vents ; in the bay to the
right the upper gate is wanting.
Canal falls or weirs are required at intervals along a canal
which has a gradient that is less than the slope of the country
through which it runs. If the canal is navigable, wherever
such falls are necessary a lock has to be provided for passing
boats between the upper and lower reaches.
The once favoured form of"ogee"fa'l has been generally
condemned, as falls of this description have given endless
trouble, the principle of design being a mistaken one. "Falls"
are now usually given a vertical drop wall with a steep face
batter. There are various ways of providing resistance to the
shock of the falling water. The simplest way, and sometimes
the most economical, is to protect the weir floor, where the water
falls, with a layer of hard ashlar sufficiently strong to bear the
shock, the floor surface being at the canal bed level of the lower
reach. Sometimes a cushion of water is formed by building a
raised sill along the down-stream edge of the floor. When this
arrangement is adopted, the general floor surface may be at
canal bed level and the sill be above it. But it is more usual
to sink the floor and to make the crest of the sill coincide with
the canal bed, as in Fig. 56. Sometimes the ctlshion of water
O 2
196
IRRIGATION.
is formed by s!iiking the floor immediately below the fall and
sloping it up to the level of the canal bed at the down-stream
edge of the floor, as in Fig. 57. In the case of weirs on navi-
gable canals the crest of the drop wall is often raised above the
canal bed level of the upper reach, and the water level is some-
times also regulated by planks sliding in iron or masonry
grooves above the weir crest, as in Fig. 56.
On the Bari Doab Canal in India many of the drops of the
CANAL FALL
WITH WATER CUSHION
Sca/e
10 6
iiiiiiiiiir
40 SO
I I feet
W.L.
cq CA«^S. BED
Meju)
W.I
NOTCH FALL
ON A CANAL IN INDIA
FIG 67
W.L.
P
canal bed are effected by rapids. ' They are constructed of
boulder pitching confined in rectangular spaces by longitudinal
and cross walls of masonry. The surface boulders are bedded
in hydraulic mortar up to their shoulders and are seated on a
foundation of boulders in mortar. The change of bed level is
effected by a rapid with a continuous flat surface slope of i in 15.
Below all falls there is always the eifect of eddies and high
velocity currents to be overcome. Various forms of down-
stream wings, of pitched apron, and of revetted side slopes are
MASONRY WORKS ON IRRIGATION CANALS. I97
adopted by different designers. There are convex and concave
wings, wings splayed at all angles, and wings parallel to the direc-
tion of flow. For the pitched length beyond the masonry work
there was, not long ago, considered to be virtue in the soda-
water bottle form of a more or less pronounced curvature. In
Egypt there are a great many escapes and regulators working
under considerable heads, which, having been allowed their
own way, have scoured out deep and wide pools down stream
of the floor, to the danger of the whole work. The best remedy
for this has been found to be to make dry rubble spurs parallel
to the direction of flow, taking off from the wings. The crest
of the spur is usually at or near high water level at its meeting
with the wing, whence it slopes gently downwards. Its length
depends upon circumstances. The result of making these spurs
in many cases has been, not only to stop erosion on the flanks,
but to cause the deep pool to silt up to some extent. The
principle of these guiding spurs has been consequently adopted
in the design of new escapes. The masonry apron and pitch-
ing, instead of being horizontal in its longitudinal section, is
often given a slope downwards from the pier ends of about
I in 10, and the pitched talus is continued at the same slope.
On the apron in front of either wing a masonry footing is built
to prevent the stone spur from sliding on the floor, and the dry
rubble spurs are constructed as above described. In India the
place of the dry rubble spurs is taken by dwarf walls of
masonry. Straight wings with rounded angles at the return
walls, or wings wit^ a slight splay of, say, 30 degrees inclina-
tion to the direction of flow, are preferred by some to other
forms.
A distinction must be made between escapes which discharge
into open basins, or wide spaces, and "falls" in canals of a
regular section. In the latter case, as prevention is better
than cure, the works should be designed to prevent poohng.
It is best to hold the water in check and to forcibly keep it to
its ordained channel until it ceases to be turbulent. To allow
1 98
IRRIGATIOK.
it to spread horizontally encourages the formation of eddies.
Whether there is anything gained, beyond a water cushion to
break the falling water, by sloping the floor and talus down-
wards is doubtful, as vertical eddies are no more to be desired
than horizontal ones.
However, the form of floor shown in Fig. 57 is stated by
Mr. Buckley to be peculiarly suitable for checking the ebulli-
tions of the water and reducing it to steady forward velocity.
But this form of floor is used in conjunction with a " notch '
FORM OF NOTCH
FOR CANAL FALLS
ELEVATION
SECTION
FIQ 58
PLAN
<
Diam,' 6 =
4 times diaW' £7
fall, which works so smoothly that there are no ebullitions to
be checked. With this description of fall the difficulties of
excessive velocity and great action down stream have been
overcome. A sketch of one of these notches is given in Fig. 58
(from Buckley). On the Chenab Canal, in India, falls have
been constructed of a row of these notches cut in a breast wall.
The principle of the design is that the notches discharge at any
given level the same amount of water approximately as the
canal above carries at that level, so that there is no increase in
velocity in the canal as the water approaches the fall (except
MASONRY WORKS ON IRRIGATION CANALS. I99
for a few feet close to the notch), but a uniform flow and a
uniform depth is maintained. No heading up by planks at
these falls is either arranged for in the design or permitted.
They are, in fact, not suitable for situations where heading up
is necessary, either for the sake of navigation or for any other
purpose. The bases of the notches of the Chenab Canal
falls are at the canal bed level of the upper reach, and
the crest of the breast wall is above full supply level. At
the foot of each notch there is a lip projecting beyond the
lower surface of the breast wall, which has a great influence
in spreading the stream and determining the form of the
falling water.
In the Fayum Province, in Egypt, the distribution of the
canal water is to a great extent effected by a description of
weir, or rather collection of weirs, known as a nasbah, an
Arabic word signifying " proportion." It is an automatic
distributor of the discharge of a canal among its branches. It
is placed where a channel divides up into two or more branches,
and is made up of weirs across the heads of the branches united
into one combined work. The level of the weir sills is the same
throughout, but the width of the waterway, or length of weir
crest, in each case is made proportional to the area of land
served by the branch. Provided that the weirs have all a free fall
— that is, that the level of water in the reach below the weir is
lower than the sill of the drop wall — the distribution of water is
practically fair. The longer weirs pass rather more than their
theoretically correct discharge ; but, as a rule, the water pass-
ing them has farther to go to reach its destination than that
which passes over the shorter weirs, and will suffer some loss
from evaporation and absorption on the way. The arrange-
ment works well and gives satisfaction to the cultivators,
who are the most interested in the just distribution of the
water. The system can only be employed where the land
surface has a slope sufficient to admit of the introduction of
free fall weirs at the points of distribution in a canai. The
zoo IRRIGATION.
Fayum is the only province in Egypt where such a system
is possible.
A most important part of all regulating works is the
apparatus that controls the levels and discharges of the
canals. In out-of-the-way situations, where skilled labour and
mechanical appliances are scarce, simplicity of design is a
great desideratum. The earliest form of regulating apparatus
was probabl}' the needle or vertical closure, prevalent through-
out Egypt some twenty years ago, and still common on the
Sind inundation canals in India. In this system horizontal
wooden baulks or rolled iron joists, fixed in the masonry faces
of the vents, bear the pressure of the vertical needles. The
needles are simply baulks of timber placed vertically side by
side across the regulator vents to effect a total or partial
closure as may be desired. They are put in place or removed
by some mechanical contrivance overhead. In Egypt, a few
years ago, this generally took the form of a lever of primitive
construction, any loose timber that was handy being employed ;
the parapet wall of the regulator was made to serve as the
fulcrum. The needles were clumsy, difficult to handle, and
unsuitable where tight closures were required. The system was
from time to time improved upon in its details. A movable frame
was devised to carry the horizontals so that they could be put
in place when required. The needles also were made lighter,
and were constructed with V-shaped edges, like sheet planking.
But, in spite of these and other improvements, the system of
closure by vertical needles has died out in Egypt, and has
been replaced by the system of closure by horizontal baulks or
planks working in vertical grooves. The horizontals are easy
to handle, require few men to work them, and give a tight
closure. The pattern of plank which is now generally used is
that shown in Fig. 59. A groove of 8 to 10 inches depth
is required with this description of plank to give a sufficient
bearing on the full-section length between the end hooks.
MASONRY WORKS ON IRRIGATION CANALS.
201
The planks are raised by iron rods provided with eyes at their
lower ends for engaging the hooks. The hooks lie within the
grooves, so that the rods, as they are passed down, are sheltered
from the current flowing over the planks, and it is therefore an
easy matter to feel for and find the hook. The greatest
objection to the system of horizontals is the difficulty of
getting the planks down in deep water against a head. The
method usually employed is to drop planks into the grooves
till the top one is above water, and then to jump them down
with an iron "monkey." The grooves in which the planks work
are either cut in ashlar stone or are of cast iron. It is not
HORIZONTAL PLANK
USED FOR CLOSURE IN EGYPT
k--
f
FIG 59
.y..J
•f
8 — . I ,
SPAN ;j
usual to employ this system of horizontal sleepers, or planks,
for spans exceeding lo feet.
For larger spans wrought iron gates are substituted for the
wooden planks. But the system is only a modification of the
system of closure by horizontal wooden baulks. The gates slide
in cast iron grooves in the same way as the horizontal planks,
and are raised and lowered by means of travelling winches
overhead. A suitable height for a gate is 8 to lo feet. So
that, where the height of closure is 14 to 20 feet, a pair of
gates in each opening, working in double grooves, is provided.
There are instances of regulators with three gates and triple
gtooves in each vent. Gates of this description are provided
with rollers whose axles are fixed to the gates ; otherwise the
weight of the gates would not be able to overcome the friction
when it was desired to lower them against a head. When the
202 IRRIGATION,
gate reaches its lowest point it ceases to bear on the wheels,
and slides on to an inclined plane in the groove, so that a tight
closure is secured.
For spans over i8 feet " Stoney's " shutters, which are
counterbalanced and move on roller beds, are much in favour.
But their province is rather rivers than canals, as canal regu-
lators rarely reach the dimensions of works for which Stoney's
gates are best adapted.
For the smaller canal regulators, with sluice openings of
z to 6 feet width, a gate of wood or iron controls the dis-
charge. Screw gearing, with a capstan in some form above,
is ordinarily used for lifting and lowering these gates. Some-
times two, and even three, shutters in one vent are operated
in the same way by screw and capstan, the shutters sliding
in double or triple grooves, as in the case of gates worked by
overhead winches.
On the Idaho Canal, in the United States, the Camer6
curtain of the Seine weirs is used for regulating sluices. It
is fitted to the head of the Idaho Mining Company's canal,
which has eight openings, 8 feet wide by ig feet high. The
roller curtains, which close the openings, are made of steel
plates and angle iron to a height of lo feet from the floor,
and of pine slats, 6 inches wide, above that height. The
bottom of the curtain is fastened to a cast iron roller, on
which it is wound up by means of a chain worked by an over-
head winch. This form of closure is suitable for a sluice with
high vents where it is desirable to keep the superstructure low,
and space for housing gates above water level cannot be
conveniently provided.
In the preceding chapter, when considering the alignment
of canals, it was laid down as a general rule that canals should
be so aligned as to avoid crossing natural drainage lines as much
as possible. But it is not always possible to avoid doing so,
especially along the first section of tne canal, which lies between
MASONRY WORKS ON IRRIGATION CANALS. 203
the source of supply and the point where irrigation begins.
It is therefore necessary to provide for the passage or disposal
of the discharge of drainage lines or natural watercourses
encountered by the canal. In some cases their waters can
be diverted into new courses and a crossing be avoided. But
when this is not the most advantageous method, one of the
following arrangements must be adopted.
Local drainage of limited areas may be discharged through
inlets into the canal if the volume of water to be got rid of is
quite small. Such works are always of little importance, as
it is not permissible to deal with large volumes of water in
this way.
Where the quantity of drainage water to be dealt with is large,
it must be provided with some means of passing the canal and
of flowing forward in its natural channel beyond the point of
crossing. A drainage line in this connection signifies any
natural watercourse, such as a river, torrent, or stream, which
carries the rainfall that drains off its catchment. There are
three ways of arranging for the crossing: the drainage dis-
charge may either pass into the canal and out again on the
opposite side by a level crossing ; or it may pass over the canal
by what is called in India a superpassage ; o^ it may pass
under an aqueduct carrying the canal. The respective levels of
canal and drainage may be such that either of the two latter
arrangements may take the form of a syphon, and the terms
" superpassage " and " aqueduct " would no longer be applicable.
A superpassage is an aqueduct, but irrigation terminology in
India distinguishes between an aqueduct that carries a canal
over a drainage line and one that carries drainage water over
a canal, the latter being technically called a superpassage.
The choice between the different descriptions of work for any
particular crossing depends chiefly on the relative levels of the
canal and the drainage channel and on the respective cost. If
the canal is navigable, it must, of course, be uppermost. If
levels alone decide the matter, it would be, natural to adopt a
204
IRRIGATION.
level crossing when canal and drainage channel are at nearly
the same level, an aqueduct when the canal is higher than the
drainage, and a superpassage when it is lower. If a level
crossing is for any reason inconvenient, the drainage can be
passed in syphon under the canal, which is generally a prefer-
able arrangement to passing the canal under the drainage,
but not always so. There are some situations in which
sudden floods may bring down detritus from the hills of the
catchment and carry it into the syphon, thereby blocking the
waterway. The result may be the destruction of the S5^hon
and the breaching of the canal. Under such conditions it
would seem to be the safer arrangement to pass the drainage
in the open channel above and the canal in syphon below ; but
torrents which carry detritus along in any quantity will give
trouble in either case.
The 'most magnificent specimens of aqueducts at drainage
crossings are to be found in India. The Solani and Nadrai
aqueducts are the largest in the world. Mr. Buckley gives the
following figures, which will convey some idea of the dimensions
of these two splendid works : —
Solani Aqueduct.
Nadra] Aqueduct.
River waterway . . ,
13,000 square feet
. 2i,6oo square feet
Canal waterway
1,600 „
• 1,040
Canal discharge
6,780 cusecs .
. 4,100 cusecs.
Arches and spans .
15 of 50 feet .
. 15 of 60 feet.
Width between faces
195 feet .
1487 feet
Length
1,170 feet.
1,310 feet.
Depth of foundation below river
bed
ig feet
52 feet.
Total height . . , .
56 feet .
88 feet.
Cost
32,87,000 rupees
44,57,000 rupees
(;f2I9,000).
(;f297,ooo).
Time taken in building .
7 years .
4 years.
The existing Nadrai aqueduct replaces its predecessor, ot
insufficient waterway, which was wrecked by an abnormal
flood. A cross-section and part longitudinal section of the
new work is given in Fig. 60. It was originally intended to
MASONRY WORKS ON IRRIGATION CANALS,
205
add a sunken floor 10 feet below the river bed, but during
construction it was decided to omit this, except in the two end
spans, as the clay substratum found below the sand was con-
sidered to have sufficient resistance to scour without masonry
protection. A protective floor is, however, often added in
works of this description. The Nadrai aqueduct will serve as
an illustration of this type of work, whether aqueduct or super-
passage. The maximum drainage discharge in the upper
NADRAI AQUEDUCT
OVER THE KALI NADI
^«»* FIG 60
10 IS BO UK)
toil I I I I -H-l I I I Feet
f 7 V WX. ** .CANAL n
I II SPAWPREL I
Vv/V •
Note. Arching m Spandret
not skonim .
channel of a superpassage is, however, generally larger than
that of the canal below, requiring a modification in the design
as regards the relative dimensions of the upper and lower
waterways. The discharge which passes over the Budki
superpassage in India reaches the high figure of 34,000 cubic
feet a second. In the design and construction of such works
particular attention must be paid to the wing walls and to the
bond between the earthwork of the upper channel and the
masonry duct. The wing walls should be given ample length,
and all possible precautions should be taken to prevent any
creep of water along their faces from the upper to the lower
206 IRRIGATION.
channel, as any such defect would develop, under the constant
head of water, into a disastrous breach.
There is another respect in which liberality of design is
advisable in works which have to pass drainage discharges.
The waterway provided should be at least sufficient to pass the
maximum flood safely. But it is not always easy to determine
even approximately what the maximum flood may amount to.
The case of the first Nadrai aqueduct, which was carried away
by a flood of six times the volume which the design had
contemplated, has already been used in Chapter V. as an illus-
tration of the difficulty of calculating discharges from catch-
ments. There is another instance of a serious under-estimate
of the maximum discharge of a drainage channel on which a
design was based. A hill torrent, with a catchment area of
172 square miles, passes underneath the Thapangaing aqueduct
in Burma. The original estimate of the maximum flood was
5,347 cubic feet a second; a later calculation increased the
figure to 17,760 cubic feet a second. The Inspector-General
of Irrigation ruled that the work should be designed to pass a
flood of 24,000 cubic feet a second. The work was designed
accordingly and put in hand. While it was under construction
the Thapangaing river rose 20 feet in five hours, dis-
charging 56,273 cubic feet a second. Since the design provided
waterway for less than half this discharge, the work had to be
modified and allowance made for a discharge of 60,000 cubic
feet a second. As the aqueduct was partly built, it was
desirable to adhere to the original design as far as possible.
The design was, therefore, altered so as to provide for passing
the drainage discharge partly under the aqueduct carrying the
canal and partly across it, so that the work has become a
combination of an aqueduct and a level crossing.
A level crossing is controlled by three regulating works,
namely, an inlet to admit the drainage discharge into the
canal, an escape opposite the inlet to pass it out again, and a
regulator on the canal down stream of the level crossing to
MASONRY WORKS ON IRRIGATION CANALS. ^0^
provide against fluctuations of the canal supply, which might
otherwise be occasioned by the passage of the drainage water
across the canal. The discharge passed across in this way is
Bometimes considerable. The Rutmoo torrent, for example,
which is carried across the Ganges Canal by a level crossing,
has a discharge of about 30,000 cubic feet a second.
In the United States wood has been much used in the con-
struction of aqueducts. The wooden channels are called
* flumes," ti term commonly employed for wooden structures
which carry the water of a canal either round steep rocky
hillsides or across drainage lines. But these wooden irrigation
works belong to a pioneer stage. Not many years hence they
will be obsolete, and, like wooden battle-ships that have done
good service in their day, they will be regarded as interesting
survivals of an old order that is past. Wood will be replaced
by the more durable materials masonry and iron. There are
some remarkable instances, in the west of the States, of flumes
constructed on a steep hillside to save the cost of excavation.
They are known as " bench " flumes. The bench flume on the
High Line Canal in Colorado is over half a mile in length, with
a cross-section 23 feet wide and 7 feet deep. Its discharge is
1,184 cubic feet a second. The San Diego flume in California
is 36 miles long, which is the entire length of the canal, so
built to avoid loss by absorption.^ Some remarkable syphons
have also been made of wood.
For aqueducts of small dimensions iron is a convenient
material to use. To prevent leakage between the ends of the
iron channel and the masonry of the abutments, a junction
must be made which will have play enough to allow of the
expansion and contraction of the iron. One way of doing this
is to give the ends of the aqueduct a bearing on a cushion of
felt soaked in tallow, which is let into the stone of the abut-
ment. This is a security against a leak along the bed.
The sides also require staunching. To provide for this, lead
• " Manual of Irrigation Engineering," by Wilson, p. 358.
208 IRRIGATION.
sheeting is attached to the iron of the aqueduct along the bed
and up the sides, and grooves in the masonry made to receive
the projecting outer ends of the lead. The grooves are then
filled up round the lead with a mixture of tar, pitch and sand
poured in hot.
If, when canal and natural stream are about the same level,
it is not convenient for any reason to resort to a level crossing
as the means of passage, a syphon must be substituted either
to carry the canal under the stream or the stream under
the canal. In the latter case the work is sometimes called
a syphon aqueduct; in the former it might consistently be
called a syphon superpassage. In the irrigation literature of
the United States a syphon is usually, with more technical
accuracy, designated an " inverted siphon."
The design of a masonry syphon is affected by the following
considerations. As it has to pass below the channel of an
upper watercourse, its foundations generally descend to a
considerable depth below the land surface. The deeper they
go, the more trouble may be expected from springs over the
foundation bed during construction. The designer bears this
in mind, and gives the barrels of his syphon width in preference
to height. But a syphon is subject to upward pressure against
the roofing of the barrels, due to the head of water under which
the syphon may be working. To resist this and prevent the
pressure from lifting the crown of the syphon, there is the com-
bined weight of the masonry and of whatever water there may
be in the channel over the syphon. As it is possible that the
upper channel may be dry when the syphon is working under its
maximum head, this unfavourable condition must be assumed
as the basis of design, and such a thickness of masonry be given
over the syphon that its weight may be sufficient to overcome
the upward pressure of the water. There are many instances of
syphons blowing up in consequence of the water pressure exceed-
ing the weight of the overhead masonry. There are, however,
syphons in existence which hold together, although the weight
MASONRY WORKS ON IRRIGATION CANALS.
209
of masonry over the barrels is insufficient by itself to resist the
water pressure. These owe their continued existence to the
fact that the tensile strength of masonry joins forces with the
weight of material in opposing the lifting force. But, in design-
ing, it is advisable to provide sufficient weight above the syphon
vents to give security without taking the strength of the mortar
joints into account. The thickness of masonry that it is on this
account necessary to provide over the syphon affects the depth
to which the foundations must be carried. The ordinary rule
SUPERPASSAGE
ON THE NrRA CANAL INDIA
SECI'ION ALONG AXIS OF BAkkEL
of thumb is to make the thickness of the crown of a syphon
equal to four-tenths of the maximum head.
Various devices have been resorted to with the view of
reducing the deptn of the foundation bed. On the Nira Canal
in India a peculiar type of syphon has been adopted which makes
use of the principle of the arch to resist the upward pressure.
The syphon in longitudinal section is given the form of an arch,
so that the weight of the outer ends is utilised to resist the
upward pressure in the tubes, and the syphon roof may be conse-
quently lightened. Fig. 61 gives a sketch of this arrangement.
Another device is the ingenious one designed' for the Ravi
> The construction of this syphon has been abandoned and a " level-
crossing" substituted.
I. P
210
IRRIGATION.
syphon in India. The diagram Fig. 62 will best explain the
principle of construction. Iron straps under the inverts below
the vents are connected by iron vertical ties with horizontal
girders above. Between the girders an upper row of inverts
transmits the upward pressure to the girders, which cannot
move without lifting with them the lower inverts and super-
incumbent masonry. The weight of the inferior masonry is thus
utilised to resist the water pressure, and, therefore, the thickness
above the vents can be reduced.
i
Scale of
RAVI SYPHQN !NDIA
PART CROSS SECTION
}
1 I 2 3 4 S ,10 30
Mil l I I I I i \ I I — t
r-eft
= !■? RIVER BEP
FIQ 62
[T/K msa Qf ij diamrdt
2i interval.
TZZZZZZZZZZi
' [2 X j'a/ h' mterva/i
at i' imferva/s
There are two forms of syphon which are common. In the
one the tube is horizontal throughout, and the entry and exit
of the water take place over the sills of a vertical breast wall,
as in the sketch Fig. 63. In the other form, the ends of the
tube are sloped to effect the change of level between the
syphon waterway and the channel on either side of it, as in
the sketch Fig. 64.
The area of waterway to be allowed in a syphon depends
upon the head under which it will work and the consequent
velocity of flow. If a head sufficient to produce a velocity of
from 5 to 8 feet a second is permissible, the syplion should be
MASONRV WORKS ON IRRIGATION CANALS.
211
given a waterway which will pass the maximum discharge at
that rate of flow. It is advantageous to obtain a high velocity
of flow in a syphon, inasmuch as it keeps the barrel free
of deposit.
To avoid the difficulty of deep foundations, syphons are often
made of steel tubes, bedded, as a rule, on concrete, and some-
KAO NULLAH SYPHQN INDIA
FIG 63
I I I T Feet
M 6 ? V V
lllllllllll 1 I
Scale
60
W.L. m SOHB C«HAL
TOP Ot BAWK
^COTRHltia iraltKS ir:;ln novfl BY BOj^j^
SYPHON ON CHE NAB CANAL
Scale cf
M
10 iq 50 IM
I i I I r I I I . 1 r Feet
14— lOo' /s-106- >. ' , FIG £4
WJL. IN
times encased in it. If, however, the concrete casing is not strong
enough alone to act as the syphon barrel when the metal
perishes, there is not much gained by adding it to the tube. If,
on the other hand, it is strong enough, the internal tube might
as well be omitted in the first instance. Even the concrete
bed is sometimes omitted. A pipe syphon without any concrete
can be laid in a flowing canal in the manner described at the
end of Chapter VII.
P 3
CHAPTER X.
METHODS OF DISTRIBUTION OF WATER, ASSESSMENT OF
RATES, AND ADMINISTRATION.
When the means of distributing water have been provided
in the form of canals with a complete system of regulating
works, the problem of distribution is not thereby wholly solved.
The method of distributing water from a canal system is almost
as important a matter as the design of the works of distribution.
The full " duty " can only be got out of a given quantity of
water by the application of methods best adapted to the condi-
tions that prevail in any particular case. The subject of water
"duty" has already been dealt with in Chapter III., and the
influence of methods of distribution on the designing of canals
has been referred to in Chapter VIII.
If the supply of water in the main source is greater than the
demand, as measured by the needs of the crops to be irrigated,
the main canals will be given the necessary discharge to meet
the demand. What the discharge should be is determined by
the actual area of crop and the accepted " duty " of water for
that crop on the particular canal under consideration. If, on
the other hand, the supply of water is less than the demand,
one of two things must be done ; either the area of crop must
be limited to that which the available supply is capable of
irrigating with the accepted " duty " of water as the basis
of the calculation of the area irrigable, or else the demand
must be met by making the water irrigate a larger area than
the accepted " duty " provides for. But in the latter case,
since the area of crop matured will be larger, each acre of it
will receive less water, or, in other words, waterings at longer
METHODS OF DISTRIBUTION OF WATER. 213
intervals apart, than the accepted " duty " assumes to be most
conducive to the well-being of the crop. An example will be
given later on of the adoption of the latter alternative in actual
practice. If there are several main canals drawling from a
source of supply which is inadequate to meet the demand, and
if all the lands have equal claims to the water, the partition of
the supply would in fairness be made in proportion to the
respective areas commanded by the canal systems on which
the lands depend for their irrigation. Each system would thus
get its fair share of the available supply, and the question as
to whether the crop area should be limited, or a reduced quantity
of water per acre be allowed, could be settled for each system
independently of the others as might seem best.
When there is a sufficiency of water to satisfy everybody,
each individual cultivator might be allowed to help himself if
the water were to be given without price. But, even if there
be a sufficiency, the water supplied has to be paid for in some
form or another. The water rate may be levied on the area of
crop either brought to maturity by irrigation, or given a single
watering, or irrigated for certain months. The cultivators pay
an amount proportional to the area of crop irrigated and
dependent on the nature of the crop, some crops requiring
more water than others to bring them to maturity. The
watered field and the standing crop furnish the data required
for calculating the amount due from the cultivator. The
objection to such a mode of assessment is that the cultivator
has no inducement held out to him to economise water.
The other method of assessment is to charge the water rate
on the actual quantity of water used. This method requires
some means of measuring the water. Different forms of water
meters, or modules,, have been invented for the purpose ; but
the conditions of flow in open irrigation channels do not lend
themselves to the accuracy of measurement which is attainable
with water meters in pipes flowing under considerable pressure,
as in the case of a city supply system. Some of the modules
214 IRRIGATION
devised are ingenious, but they are only suitable for small
discharges and for use in countries, such as Italy, where the
ethics of irrigation have reached such an advanced stage of
evolution that " it is thought apparently as discreditable to
appropriate an unfair supply of water as to steal a neighbour's
horse, as discreditable to tamper with the lock of the water
module as with the lock of a neighbour's barn." *
When the supply of water is not in excess of the demand, an
economical and just distribution depends more on correct
methods of administration than on the perfection and complete-
ness of the regulating works. All countries that have practised
irrigation on a large scale have found it necessary to adopt
some system of " rotation " whereby water is alternately
supplied and withheld for fixed periods. Under this system
the total area requiring irrigation is divided up into two or
more sections, and each section in succession is given
water, while at the same time it is withheld from the other
sections. The duration of the period of supply is propor-
tional to the area of crop included in the section whose
turn it is to be watered. The more perfect are the
methods of administration and the means of regulation, the
more minute can be the subdivision into sections, and
the more exact will be the just distribution of water. But
there are practical considerations which impose a limit on
the subdivision. The operation of irrigating a single acre
takes a certain time, say two hours, and requires a certain
discharge, say 2 J cubic feet a second, to complete the watering.
Theoretically , double the discharge should complete the
irrigation of the acre in one hour, but practically the cultivator
would find that he could not lead the water about his field at
the pace required to complete its irrigation in this short time.
As a rule, the subdivision does not go so far as to create
sections of so small an area as a few acres ; but in Italy, for
instance, where distribution of water is carried out in a more
* Colonel Sir C. Scott-Moncrieff s address, British Association, 1905.
METHODS OF DISTRIBUTION OF WATER. 215
perfect manner than in any other country, the sections are so
small that the duration of the supply periods is reckoned by hours,
and not by days; Each cultivator is allowed the use of the water
for a number of hours proportional to the area of his crop, and
pays, according to the area he waters, his contribution towards
the total cost of the maintenance of the irrigation system, and
his share of the sum which has to be paid to the Government.
In France also the rotation periods are measured in hours.
Whatever the area may be, water is supplied to cultivators at a
constant discharge of 30 litres (i'o5 cubic feet) per second.
The period of flow allowed is reckoned at the rate of five hours
per hectare (two hours per acre). As the land is much subdivided
and the irrigation has to be continued by night as well as by
day, the rotation programme is so drawn up that the same
people may not always get their turn during the night. This
is arranged for by making the interval between waterings so
many whole days and a fraction of a day, the odd hours being
introduced for a similar purpose to the dog-watch on a ship.
The intervals between waterings, in the case of land devoted
to market gardening, are from six to seven days. The irrigation
season lasts about six months, so that about thirty waterings are
given to the irrigated lands. With intervals between waterings
of six and a half days, and allowing five hours per hectare, a
discharge of 30 litres (i"o6 cubic feet) per second would irrigate
an area of 30 hectares (74 acres) of crop. The allowance
made provides a volume equivalent to a depth of 2^ inches
over the whole area irrigated for each separate watering.
In Spain also the distribution periods are sometimes measured
in hours. The irrigated lands of the Henares valley, for example,
are divided into plots of about 800 acres. Each plot is served
by a branch canal taking off from the main canal. The branch
canal is fed through a module, a continuous discharge at the
rate of i cubic foot a second for every 156 acres being allowed.
The fields are irrigated by a number of distributaries taking off
from the branch canal. The whole discharge of the branch
2l6 IRRIGATION.
canal is turned into each distributary in succession, and each
individual landlord or tenant is given the water for a period,
measured in hours and minutes, proportional to the area of the
crop on his holding. In this way each separate holding gets a
watering at regular intervals.
In India the rotation system, copied from Europe, is known
among the natives as irrigation by tatils ; Egypt copied it from
India, and the fellah calls it irrigation by manawabah ; in
Java, where also it is practised, it is called the golongan system,
all these expressions signifying irrigation by turns.
The advantages of such a system are many. By concen-
trating the available supply in half, or a third, or a less fraction
of the canals, and giving the whole of it to the section whose
turn it is to take water, the irrigation is made easy in conse-
quence of the higher water levels produced in the canals. At
the same time, in the other sections which are not receiving
water, the danger of the canals causing waterlogging of the soil
is removed, as they are either empty or flowing at a low level.
The crops require water at certain intervals, and not con-
tinuously. It is better for them, as soon as they have received
a watering, that the water supply should be shut off from their
neighbourhood, so that all excess of water, over and above that
used up or absorbed, may be got rid of, and not be allowed to
stagnate. Irrigation by rotation, moreover, is a system that
conduces to economy of water. For the water is delivered just
where and when it is wanted for irrigation, and is therefore not
allowed to run to waste. The loss from evaporation and
absorption is less, as the water is spread out over a less extent
of canals. The irrigation staff can superintend the distribution
more thoroughly, as their exertions can be wholly devoted to
the section under irrigation for the period of its supply. The
cultivators also find such an arrangement a convenience, as
they know exactly when they must arrange to water their fields.
Moreover, the velocity of current of the canals, when in flow,
is maintained at a high rate in consequence of the fuller
METHODS OF DISTRIBUTION OF WATER. 217
discharge, whereby more of the silt is carried forward to the
fields and less deposited in the canal. Lastly, the system
ensures an equitable distribution of the water to all cultivators,
and offers such facilities for reducing the amount of waterings
given in a season of short supply that the drawbacks of a
deficient supply can be made to bear equally on all, with a
minimum of disadvantage to anyone.
In India there are two modes of applying the rotation
system. One arrangement is that in which all the distributing
:anals are kept in continuous flow, and the outlets, supplying
the village channels, are opened and closed by turns. The
outlets are grouped into two or more sections, and each section
is allowed to take water for a certain number of days in its
proper turn. The other and better arrangement is that in
which the distributaries are subjected to rotation. As with the
outlets, they are grouped into sections, and each section in turn
flows with full discharge while the others are closed. Sometimes
a combination of these two arrangements is adopted, and rota-
tions are applied to groups of distributaries, and again to groups
of outlets on those distributaries. " In the simplest cases,
where only the outlets from the distributaries are tatiled, it is
usual to divide the distributary into three lengths, so that the
village channels taking off each length command areas which are
approximately equal. The outlets in the first length of the
distributary usually get water for three days in each week, and
are closed for four days. The outlets in the second length of
distributary are open on the four days when those in the first
length are closed, and closed on the three days when the others
are open ; in the third, length of the distributary the outlets to
the village channels are allowed to be open all the week as a
rule, and they absorb all the water passed on by the upper
lengths" (Buckley).
When the distributaries are subject to rotation, the pro-
gramme has to be drawn up to cover longer periods, and it
becomes more complicated. The recent history of irrigation
2l8 IRRIGATION.
in Egypt furnishes a good example of this alternative method
of applying the rotation system.
In Egypt the severest application of the system of irrigation
by turns was made in the summer of igoo, when the scantiness
of the available water supply, in relatione to the requirements
of the cultivated area, exceeded all previous and subsequent
experience. ' The irrigation officers were faced with this
problem. There was a certain area of land under cotton
which had to be irrigated ; there was an insufficient and con-
stantly diminishing supply with which to irrigate it. The
Assuan reservoir was not as yet in existence. The crop, that
was in danger of suffering for want of timely irrigation, was
cotton, on which the wealth of modern Egypt principally
depends. The cotton plant, during the season of low supply
in summer, requires watering at intervals of eighteen days. It is
generally believed that the yield is diminished if the intervals
between waterings are prolonged beyond eighteen days. But, in
the summer of igoo, there was not enough water in the river to
complete one watering of the whole cropped area in so short a
period. There were then only two possible alternatives to
choose between : either the area of crop to be irrigated must be
reduced to that which the discharge was capable of watering in
eighteen days, or a longer time for the watering must be allowed.
The practical impossibility of reducing the crop area, once it
had been planted, without doing injustice to individuals, caused
the rejection of this alternative. It, therefore, remained to
arrange a programme by which sufficient time should be allowed
for the irrigation of the whole area of cotton crop. A given
discharge takes a definite time to irrigate a given area, and, as
the discharge decreases, the time of the operation must increase;
that is, in other words, the intervals between the waterings of
any particular field must be longer. It was found a convenient
arrangement to divide each separate system of canals into three
sections, which were designated A, B, and C. Now much of
the irrigation was effected by pumps, which, it was calculated,
METHODS OF DISTRIBUTION OF WATER.
219
could complete the irrigation of all the crops depending on them
in six days, but not in less. So six days was accepted as the
period of working for each section. If the water supply had been
sufficient to irrigate the whole cropped area in eighteen days,
each section would have taken water in turn for six days, and have
been prevented from taking it for the succeeding twelve days ;
that is, the interval between waterings for any particular field
would have been eighteen days. But it was found that the supply
was only sufficient at first to give one watering in twenty days,
and later on in twenty-four days, and still later, at lowest supply,
in twenty-eight days. To arrange for the twenty-eight days'
rotation, it was necessary to rearrange the subdivision and to
group the canals into four sections, which were called D, E, F,
and G, to avoid confusion with the threefold arrangement.
The programmes of rotation were, then, made out on the
following basis : —
Three Sections.
One watering One watering
in 20 days, in 24 days.
Section A takes water
General stoppage
Section B takes water
General stoppage
Section C takes water
General stoppage
6 days 6 days
In 2 - „
6 11 6 „
I „ 2 „
a „
B and C stop.
A and C stop.
A and B stop.
20 days 24 days
Four Sections.
One watering in 28 days.
Section D takes water
General stoppage .
Section E takes water
General stoppage .
Section F talces water
General stoppage .
Section G takes water
General stoppage .
6 days
I l>
6 „
I »
6 „
1 »
6 „
E, F, and G stop.
D, F, and G stop.
D, E, and G stop.
D, E, and F stop.
a8 days
.
2^10 IRRIGATION.
The general stoppages of one or two days were intended to
provide for the filling of the channels of the section whose turn
to work came next, so that the water might reach the tail ends of
the sections, and the pumps at the tails have as good a supply
from the commencement of their six-days period as those higher
up the canals. These intermediate general stoppage days were
also used to give water to those who had been badly supplied
during their proper working period. It was moreover arranged
that, if the tail reaches of any section did not get water in their
proper turn, they should be given water with the section whose
turn came next. By so arranging, it became possible to get
water to them, since all the pumps or heads above them on the
same branch were stopped. The intermediate days of general
stoppage provided a reserve which could be utilised to prevent
arrears accumulating to such an extent as to upset the published
programmes and introduce confusion during the most critical
period.
In the summer of 1900, in Egypt, the supply was so short
that, if the cotton crop was to be saved, provision could not be
made for rice irrigation, and as the rice crop in comparison
with the cotton crop was of little importance in both extent
and value, it was sacrificed to the needs of the more valuable
crop. By such measures as described, the cotton crop was
irrigated by a discharge of 21 cubic metres a day per acre,
instead of the normal 30 cubic metres a day which is the
discharge required to allow for waterings being given every
eighteen days. The latter is the " accepted duty," as has been
explained in Chapter III.; the former represents the actual work
done by the water in the summer of igoo. According to the
accepted " duty," i cubic foot a second should irrigate 81^ acres ;
in the summer of 1900, i cubic foot a second was made to irrigate
116 acres, or more than 42 per cent, in excess of the " accepted
duty." "■ But, under these circumstances, some of the crop
suffered in yield from insufficiency of water, and so the season's
apparent "duty" included duty imperfectly performed in
METHODS OF DISTRIBUTION OF WATER. 221
consequence of the water having been called upon to do work
beyond its powers.
After the experience of a succession of low summers in
Egypt, the conclusions arrived at, as to the best programme for
rotations, is thus stated in the Irrigation Report of Egypt for
igo2 : — "As a consequence of previous experience, it has been
decided in 1903 to adopt the three-section arrangement of
distribution, by which each section takes water in turn for a
third of a full period, which has been fixed at eighteen days ; so
that each section will get water for six days, and be without it
for twelve. For canals, however, from which rice is irrigated,
two sections are adopted, each section working for four days and
stopping for five. The day when neither section works comes
after the working of the first section, and is utilised for filling
the channels of the second section before water is drawn oft
from them. As the rice full period is half of the cotton period,
a cultivator may, if he likes, raise cotton or rice, or both.
Supposing he has an area of 200 acres to put under crop,
he can put it all under rice and irrigate it once in nine days ;
or he can put it all under cotton and irrigate 100 acres
during one turn and 100 acres during the next, so that one
watering in eighteen days is given to it all. Or he may put
100 acres under rice and 100 under cotton. In this case he
would irrigate all the rice and 50 acres of cotton during one
turn ; and all the rice again and the other 50 acres of cotton
the next turn : so that, in every case the rice would get a
watering in nine days, and the cotton in eighteen days. The
cultivator is thus free to plant what he likes."
This programme contemplated assistance from the Assuah
reservoir, which had been completed in 1902. Without such
assistance, the period of eighteen days would have had to be
increased to twenty-one, and later to twenty-four, days by
inserting one or two days of general stoppage between each
section's period of working, as was done in 1900. With a
period of nine days between waterings of rice, and of eighteen
222 IRRIGATION.
days between waterings of cotton, the discharge required at the
canal head was found to be at the rate of 30 cubic metres (1060
cubic feet) a day per acre of cotton crop, and at the rate of 60
cubic metres for rice. If the supply falls short of these allow-
ances, there are, as has already been stated, only two ways of
meeting the deficiency of supply, namely, either by lengthening
the intervals between waterings or by reducing the area of
crop to be watered. The former is sometimes the only,
practicable alternative.
If the other alternative of reducing the area of crop is
adopted, the reduction must be determined upon before the crop
is sown or planted. Sir Colin Scott-Moncrieff, in his address
at the Meeting of the British Association, 1905, already quoted,
thus describes the system of distribution under the " Irrigation
Association West of the Sesia," in Italy: "To effect the
distribution of the water the area irrigated is divided into
districts, in each of which there is an overseer in charge and
a staff of guards to see to the opening and closing of the
modules which deliver the water into the minor water courses.
In the November of each year each parish sends in to the
direction-general an indent of the number of acres of each
description of crop proposed to be watered in the following
year. If the water is available the direction-general allots to
each parish the number of modules necessary for this irrigation ;
but it may quite Well happen that the parish may demand
more than can be supplied, and may have to substitute a crop
like wheat, requiring little water, for rice, which requires a
great deal."
In certain districts of India it is considered desirable to
restrict the area under irrigation to a certain proportion of the
area commanded. * When the available supply of water is
insufficient to irrigate the whole cultivable area commanded,
such a restriction is desirable for the sake of distributing the
water to as many parts of the district as possible for the
benefit of the people. But there is another reason for the
METHODS OF DISTRIBUTION OF WATER. 223
restriction. If irrigation is spread over all the area commanded,
the soil, when light, is liable to become water-logged, and the
spring levels may be unduly raised.
In the discussion on the Irrigation Papers read at the
International Engineering Congress of 1904, at St. Louis,
Mr. J. E. de Meyier describes the system of rotation, or
golongan system, as practised in Demak, Java: "The fields
are divided into four, iive or six classes : those of the second
class get the water a week later than those of the first ; those of
the third a fortnight later, and so on." Mr. de Meyier gives the
following example to explain the system, taking a quick
growing kind of rice as the crop of his illustration. " The rice
fields are under irrigation for nineteen weeks. For the first
two weeks of this period the discharge required for the pre-
liminary operation of ploughing is at the rate of i cubic foot a
second for every 50 acres. After the ploughing the rice is
sown on about a tenth of the area to form nurseries for the
seedlings, which will afterwards be transplanted to cover the
whole area. The nursery period lasts five weeks, and during
this time the discharge needed is at the rate of i cubic foot a
second for every 50 acres of nursery area, with an addition of
I cubic foot for every 2,000 acres of the whole area to allow for
further tilling operations. After transplanting the seedlings to
the larger area, an increased supply at the rate of i cubic foot a
second to every 150 acres for a week, and then at the rate of i
cubic foot a second to about every 80 acres for three weeks, is
required ; and thereafter a gradually diminishing supply till the
nineteenth week. If then, for instance, the total area of the
rice fields is 10,000 acres, and if the whole of it is taken in
hand at once, the discharges required will be those represented
by the figures of the second column of the accompanying table.
Now supposing the river from which the supply is drawn never
discharges more than 95 cubic feet a second, and that it
continues to flow, though with diminishing volume, for, say,
twenty-five weeks, how are the 10,000 acres of rice crop to be
224 IRRIGATION.
irrigated under these conditions, seeing that for seven weeks out
of the nineteen a greater discharge than 95 cubic feet a second
appears, from the figures in the second column of the table, to
be necessary? The method of solving the problem is this:
The 10,000 acres of rice field are divided into five sections, A,
B, C, D, and E, of 2,000 each. For the first two weeks
sections A and B get the full discharge required for the
preliminary operation of ploughing, and the other three sections
are left alone. In the third and fourth weeks sections C and
D, and in the fifth and sixth weeks section E, get in their turn
the full discharge required. For the five weeks succeeding the
ploughing, each section successively gets the reduced supply
required for its nursery, and after that an increase when the
seedlings are planted out, followed by a decrease as the plant
becomes mature. But in sections D and E the nursery stage
has to be prolonged to six and seven weeks respectively on
account of the limited supply not admitting of an increase at
the end of five weeks."
"The table on the next page shows this method of over-
lapping, whereby it is arranged that the total discharge
required at any time never exceeds the river discharge of
95 cubic feet a second. The figures in the last column give
the aggregate daily discharges required by the five sections,
week by week, for the twenty-five weeks of the rice-cultivating
period."
As a contrast to systems of rotations which have been devised
to do equal justice to all concerned, the custom of "priorities"
of the United States is worth notice. The law recognises the
prior right of first comers to be first served with the water of
running streams to the extent to which they put it to profitable
use. The man who first made use of the water of any stream
to cultivate a certain area is, by custom and law, entitled to
withdraw the same quantity of water when his land requires it,
without regard to the interests of his neighbours. The man
who followed him, at no matter what interval of time, has a
METHODS OF DISTRIBUTION OF WATER.
225
secondary right, and may in future withdraw from the stream
the amount of water originally used to cultivate his farm,
provided there is sufficient to first supply the prior settler.
The man who is third in point of time can utilise his share only
Supply in Cubic Feet per Second.
The Area divided into Five Sections of 2,000 Acres each.
Number
The whole
Area of
10,000 Acres
Aggregate
Supply
Required.
of Week,
Section
at once.
A.
B.
c.
D.
E.
I
300
40
40
_
.„
_
80
2
300
40
40
—
—
—
80
3
25
5
5
40
40
—
90
4
25
5
5
40
40
—
90
5
25
5
5
5
s
40
60
6
25
5
5
5
5
40
60
7
25
5
5
5
5
5
25
8
80
16
16
5
5
5
f7
9
120
34
24
5
5
5
63
10
120
34
34
16
5
5
74
II
120
24
34
24
16
5
93
12
100
20
30
34
24
5
93
13
100
20
30
34
34
5
93
14
75
15
15
30
24
16
90
15
75
•15
15
30
20
24
94
16
50
10
10
15
30
34
79
17
50
10
10
15
15
34
74
18
25
5
5
10
15
20
55
19
25
5
5
10
10
20
50
80
—
—
—
5
10
15
30
31
—
—
—
5
5
15
25
32
—
—
—
—
5
10
15
23
—
—
—
—
—
10
10
34
—
—
—
—
—
5
5
25
—
—
■""•
~
5
5
after the first and second men have had their prior claims
satisfied ; and so on, the late comers being compelled, if neces-
sary, to leave the water untouched until all with prior rights
have had the full quantity which is their legal due. As the
country develops under the stimulus of irrigation, there is a
growing tendency to abandon the observance of priorities, and
h Q
226 IRRIGATION.
io adopt the principle of distribution according to areas of crop
or cultivated land.
When the delivery and distribution of a water supply is
effected by an artificial system of canals, it is usual to charge
for the irrigation by water rates in some form or other. In
Java, however, there is no water rate or charge for water. The
rainfall of the island is considerable, and it would be difficult to
estimate to what extent a full supply from canals benefits the
crops which hitherto had depended mostly on rain assisted by
a scanty allowance of irrigation water. The land ia.x is
assessed in relation to the average yield of the crops grown,
which depends on the fertility of the soil and the nature of the
water supply. When the water fails, a partial remission of the
tax is allowed. The land tax assessment and collection thus
takes account of the irrigation supplied, and no additional
water rate can be levied.
In Egypt also there is no Government water rate. Payment
of the land tax confers the right to a supply of water sufficient
for the maturing of one crop during the year, and imposes on
the Government the obligation to make that supply available.
If the Government fails to do so, the land tax is remitted. The
only measurements made are of those areas which have
remained without water throughout the year from no fault of
the cultivator, and on which the land tax has, therefore, to be
remitted. The irrigation officers of Egypt are thus relieved of
all the troublesome revenue work which adds so much to the
duties of the irrigation staff in India.
The rates charged in India for the water required to mature a
crop vary from i rupee an acre for rice to 20 rupees an acre for
sugar-cane. The average rate for thewhole of India is rather more
than 3 rupees an acre for the revenue realised, and in addition
I rupee an acre for working expenses. Compared with the
value of the crops raised by irrigation the water rates charged
in India, if not low, are decidedly moderate. But in India as
METHODS OF DISTRIBUTION OF WATER. 227
a rule the crops are not wholly dependent on the canals, as, to
a varying extent, rainfall supplies the water needed. The
water rate may therefore be considered to be made in return
for a guarantee that sufficient water shall be supplied to ensure
the maturing of the crop. But in Sind, where crops are grown
only on irrigated land, and where landi without water is value-
less — the conditions being much the same as in Egypt — there
is no separate charge for irrigation. As in Java and Egypt, the
assessments of the land revenue are made on the basis of the
average produce, and account is thus taken of the increase of
yield due to irrigation. This system of a " consolidated " rate
is followed also throughout the Madras Presidency, in certain
districts of Burmah, and also in some parts of Bombay depend-
ing on old irrigati on works.
In the Western States of America, where the rainfall is less
than 20 inches per annum, a water rate is charged of from
£2 8s. to £4 per acre, the farmer paying in addition a rate of
from 2S. to los. per acre annually for maintenance. In
comparison with India these rates appear high.
In Piedmont in Italy the farmer pays, according to the area
he waters, his share both of the sum which is due to the govern-
ment and of the cost of maintaining the irrigation works. The
Government charge per annum is at the rate of 800 liras per
module of 2'047 cubic feet per second delivery, or £15 12s. yd.
per cubic foot per second.
In France the association or syndicate that manages the
canals charges a water rate on the basis of a continuous flow
of I litre per second per hectare. The rate varies from 35 to
70 francs per annum per hectare, equivalent to 12s. to 24s.
per acre.
In Spain the price of water varies considerably. The
followers of the conquerors who expelled the Moors pay
nothing for the irrigation works that serve the lands granted
to them in reward for their services, excepting only a small
annual tax to cover the cost of maintenance. The same
Q 2
228 IRRIGATION.
privilege is enjoyed by all the land-holders of the irrigated
plain of Valencia, " according to what had been anciently
established and practised from the times of the Saracens."
Otherwise irrigation is paid for either by the year or for a
single watering. The price of a single watering — reckoned as
consuming i8o to 200 cubic metres per acre — varies in Alicante
from lod. to 21s. an acre ; in Lorca the price is los. an acre, in
Almansa is., in Granada is. 8d. to 3s. 5rf. When irrigation is
paid for by the year, the annual charges are as follows: in
Catalonia, on an average, lis. 2d. an acre; on the canal of
Urgel and at Malaga 19s. ^d. ; on the Esla canal £1 ; and on
the Henares canal ^i 9s. The wide range in price for a
single watering in Alicante is due to variations in the amount
of the available supply and in the dryness of the season.
In countries where the agricultural classes are for the most
part little educated, it is best for all interests that the control
of the irrigation should be in the hands of the Government.
In Egypt and in the British possessions in India irrigation is
so administered. The responsibility for the construction of the
canal works, and for the just and economical distribution of
the water, rests with supervising officers of the higher grades
in the irrigation service. On the character and ability of these
ofificers depends the successful and satisfactory working ot
Government irrigation systems. In India and Egypt this
condition of success has not been wanting ever since British
engineers have been the responsible officers.
The duties of the Government irrigation engineers are
manifold. • They elaborate, the project for the irrigation of a
tract of country, and design the works of supply, distribution
and drainage ; they arrange for and superintend the con-
struction of the works; and, lastly, they control the water
distribution of the completed canal system, and the assess-
ment of the water revenue derived from its working. As part
of the irrigation system the flood banks of the river are in their
METHODS OF DISTRIBUTION OF WATKR. 229
charge, to be maintained as a defence against inundation of
cultivated land. Associated with the maintenance of flood
banks, training works for the control or improvement of a river
have often to be undertaken. Inland navigation, whether on
natural waterways or on artificial channels, falls under the
care of the irrigation officer, at any rate in India and Egypt.
Land reclamation by drainage works and by pumping may also
be added to the list of his duties. In India he may even be
called upon to do magistrates' work, and try cases and sentence
offenders under the Irrigation Act.
The Irrigation Branch of the Public Works Department in
India is thus constituted : A chief engineer is at the head of
the establishment of the province ; under him are superintend-
ing engineers of "circles," who have jurisdiction over areas
including 500,000 to 1,000,000 acres of irrigation : next come
the executive engineers, who control " divisions," comprising
sometimes 200,000 acres of irrigation. The executive engineer
is the officer who is responsible for the proper assessment of
the irrigation revenue ; it is his duty also to arrange for the
repairs of the works, to prepare projects for the improvement
of his division, and to secure the proper regulation and
distribution of the canal water. He is assisted by a large
establishment of Government officials, chiefly composed of
natives of India, who live in the various " sub-divisions " and
" sections " into which the division is divided.
In Egypt the Irrigation Department is a branch of the
Public Works Ministry, which is under a minister, assisted by
an under-secretary of state. The irrigation service is under
two inspectors-general, one for Upper Egypt, and the other for
Lower Egypt. Under the inspectors-general are inspectors
of irrigation, and under them again directors of works and chief
and district engineers. Each inspector-general's charge com-
prises from 3,000,000 to 3,500,000 acres of irrigated land. The
inspectors of irrigation have charge of " circles," comprising
areas of 500,000 to i.ooo.ooo acres. The controlling staff
230 IRRIGATION.
includes also an inspector-general for headquarters and another
for basin conversion works. The duties of an inspector of irriga-
tion in charge of a circle are, if not the most important, at any
rate the heaviest of all.
Java is in a transition stage as regards methods- of adminis-
tration in irrigation matters. Experimental establishments,
regulations and methods of distribution do not seem as yet to
have led to any definite conclusions as to what is the best to
adopt. The general idea on which the experiments are based
is to divide the island into fourteen irrigation circles, each of
which would contain the entire catchment basin of one or more
rivers, irrespective of the political frontiers of the provinces.
Each circle would be put in the charge of an engineer with a
proper staff. The circle engineers would be under the chief
engineer, who is the head of the public works division, and
they would be the technical advisers of the residents and
their provincial officers. The experimental organisation of
the Javan irrigation service has points of resemblance to the
administrative arrangements of both India and Egypt.
Though it may be best for countries with native agriculturists,
such as those of India and Egypt, to have their irrigation
administered by Governi^ent, it does not follow that there is
not a better way for countries with an agricultural class more
advanced in civilisation. A good example of self-government
in irrigation matters is given by Sir C. Scott-Moncrieff in his
British Association Address, already quoted from more than
once. He describes how these things are managed in Pied-
mont, in Italy : " The Irrigation Association west of the Sesia
takes over from the Government the control of all the irrigation
lying between the left bank of the Po and the right bank of the
Sesia. The Association purchases from the Government from
1,250 to 1,300 cubic feet per second. In addition to this it has/
the control of all the water belonging to private canals and
private rights, which it purchases at a fixed rate. Altogether
it distributes about 2,275 cubic feet per second, and irrigates
METHODS OF DISTRIBUTION OF WATER. 23 1
therewith about 141,000 acres, of which rice is the most
important crop. The ^Association has 14,000 members and
controls 9,600 miles of distributary channels. In each parish
is a council, or, as it is called, a consorzio, composed of all land-
owners who take water. Each consorsio elects one or two
deputies, who form a sort of water parliament. The deputies
are elected for three years, and receive no salary, » The
assembly of deputies elects three committees — the direction-
general, the committee of surveillance, and the council of
arbitration. The first of these committees has to direct the
whole distribution of the waters, to see to the conduct of the
employis, etc. The committee of surveillance has to see that
the direction-general does its duty. The council of arbitration,
which consists of three members, has most important duties.
To it may be referred every question connected with water
rates, all disputes between members of the Association, or
between the Association and its servants, all cases of breaches
of rule or of discipline. It may punish by fines any member of
the Association found at fault, and the sentences it imposes
are recognised as obligatory, and the offender's property may
be sold up to carry them into effect. An appeal may be made
within fifteen days from the decisions of this council of arbitra-
tion to the ordinary law courts, but so popular is the council
that, as a matter of fact, such appeals are never made."
In Spain there exists a parallel to the Piedmont method of
administration. The irrigation syndicate of Valencia was the
first " tribunal of waters " to be created specially for the trial
of irrigation cases. It sits in the open air, upon the porch of
the side door of the Cathedral, and settles all questions relating
to irrigation that are brought before it. There is no appeal
against its decisions. The institution, which is of Moorish
origin, is very popular in Spain, and has been imitated, with
more or less success, by all the other syndicates of the
country.
The regulations concerning the granting of irrigation
232 iRRlGATlOtt.
concessions in Spain contain a condition which is worthy of
special note. The prospective irrigators are bound to form a
syndicate among themselves, even when the water supply is
conceded to a company which is authorised to recoup itself for
ita outlay by levying an annual payment for a fixed number of
years. The syndicate, on the one hand, is better able as a body
to protect its own interests in its dealings with the company
than individuals would be ; and, on the other hand, the com-
pany's relations with the irrigating community are facilitated
by their having a duly recognised body of representatives to
deal with.
The system of canal management in France is in some
repects similar to that of Spain. None of the canals of
Southern France belong to Government. With the exception
of the case of the Marseilles Canal, the usual agency by which
canals are constructed and administered is an association of
cultivators. The desire of the French Government is that
those who use the water should organise themselves into
associations, or syndicates, with authority to construct and
work irrigation canals at their own risk. The Government aids
the undertaking by contributing about one third of the estimated
cost of the work, and supervises the work as far as it considers
necessary.
In America no well-devised scheme of canal administration
has as yet been evolved, but there is a tendency to admit the
necessity for public control of irrigation. The pioneer settlers,
when they first made use of the water of a running stream for
irrigating their land, were not under the restraint of any regula-
tions as to the time of opening and shutting the head-sluices,
but pleased themselves about it. When the needs of others
compelled the introduction of some management of the water
supply and the drawing up of regulations as to its use, the
farmers, who inherited from their pioneer predecessors their
habits of freedom to do as they liked, were slow to submit to the
imposed restiaint. When application to the law courts failed
METHODS OF DISTRIBUTION OF WATER. 233
in its effect, the irrigator, who was deprived of his supply of
water through illegal use of it by someone higher up the stream,
had no other course left open to him but to shut down the
offender's head-sluice by force. Mr. Elwood Mead in his paper
read at the International Engineering Congress, 1904, gives an
example of such a case. A canal owner in California was
asked how he managed to protect his rights in the
seasons of shortage ; he replied that, in the first place, he had
obtained a decision establishing his legal title to water; but
that, in addition, every year he shipped in two men from
Arizona who were handy with a gun, and that between the
courts and the guns he managed to get his share. To which
Mr. Mead adds this comment : " Peace and prosperity for the
individual and the community alike depend upon public control
of the streams and the enforcement of laws by men of
experience and administrative ability of a high order. The
greatest weakness of American irrigation has come from the
failure to recognise this." Six States have, however, intro-
duced government administration of canals, but the systems
differ so widely from one another that a general description
applicable to all cannot be made. Still, the policy of one State
may serve as an illustration. According to the Wyoming code,
the water of canals, streams, springs, lakes and ponds is State
property. The State Engineer is the president of a board of
five men managing this property. The State gives irrigators
free use of the water, permits for this being issued by the State
Water Board. It is a misdemeanour to take water without such
a permit. To secure it intending users of water must file a
map and description to show the position of the proposed
channel or reservoir and the land to be irrigated. Permits are
refused for any project which would cause injury to an existing
right. But when permits are granted, after the water has been
actually applied to the land, the State issues a certificate of
appropriation which describes the land in question. These
certificates are recorded in the same manner as land laws. In
234 IRRIGATION
order to protect the rights thus bestowed, the State has to
control the distribution of the water when there is not enough
for all. For this purpose the State is divided into four divisions,
and these are sub-divided into forty districts. Each district
has a water commissioner, a State official acting under the direc-
tion of the State engineer. In times of deficient supply he
raises and lowers the gates in such a manner as to give each
channel its proper share. Head-gates adjusted by the com-
missioner may not be moved by the owner. The commissioner
has authority to arrest offenders, or he can call on the sheriff to
do so. As" Mr. Mead remarks, it is always difficult to induce
irrigators to submit to this public control, but, once adopted, it
is always maintained. It relieves irrigators from watching their
neighbours. They do not have to patrol the stream at night to
prevent gates being raised when they should be closed. Where
irrigators have to defend their own rights, neighbours are always
at war. Where there is public control they live in friendly rela-
tions with each other, while the water commissioner is often
abused. If he does his work with tact and justice, he becomes
the most important member of the community, and contributes
to its respecf for law and order, and to the peace of mind and
well-being of the irrigators to a degree which has to be
experienced to be understood.
Those who have had experience of irrigation in Eg3^t during
the British Occupation will understand these remarks well.
Before a real control was exercised over the distribution
of water by engineers of experience and honesty, the native,
irrigators, during the period of water scarcity, used to settle
among themselves all irrigation questions by breaking each
other's heads with nabouts, a stout stick of a kind convenient
for the purpose. When the inspector of irrigation (corre-
sponding to the water commissioner of America) assumed
effective control of the working of the canals, the summer death-
rate due to water disputes declined, and, before long, perfect
confidence in the inspector's justice and ability was established,
METHODS OF DISTRIBUTION OF WATER. 235
It is seldom now that any agriculturist in Egypt in want of
water takes the law into his own hands.
But before all else, as a preliminary to any scheme of canal
administration, the right of the public to the natural water
supply of the country must be safeguarded against any exclusive
appropriation by individuals. This important duty should not
be neglected or postponed by the Government of any country
that is endowed with the means of development that irrigation
brings. Rivers, torrents, streams, and all natural water-
courses, and the water that flows in them, should be declared
by decree to belong to the public domain. In Italy and Spain
the example has been set for other countries. In India and
Egypt no one would think of contesting the Government's
right to possess the country's natural waterways. According
to the Wyoming code in the United States, which served above
as an example of State administration, the water of canals,
streams, springs, lakes and ponds is made State property-
France has stopped short of a thorough-going State policy in
respect to the ownership of its watercourses : for, though irri-
gation is indispensable in the south of France, it is not so in
Northern and Central France. The country as a whole is
more interested in navigation than in irrigation. Consequently
the waterways that are navigable by boats or rafts, whether
natural or artificial, are declared to be the property of the
State. Other watercourses belong to no one, but the riparian
owners of land have the right of using the water. Nevertheless
the Government exercises a supervision over all these water-
ways, and no water can be taken for purposes of irrigation
without a special permit signed by the prefect of the
department.
Sir William Willcocks, in his Report on " Irrigation in
South Africa, 1901," lays stress on the necessity of establishing
by decree that all rivers and natural watercourses are part of
the pubhc domain. The longer this action is postponed the
greater will be the difficulty of taking it, as vested interests to
236 IRRIGATION.
be overcome will grow in number and strength with the
development of the country. More especially is it necessary
to take this step in South Africa, as the only possible means of
promoting the agricultural development of the country seems
to be by means of water storage ; and, if water storage is the
solution of the agricultural problem, Government must under-
take the work. The construction of dams and the formation
of reservoirs with their distributing canals are undertakings too
vast for private enterprise, and they affect the prosperity of so
wide an area that the State should assume the responsibility
for their construction and subsequent management.
CHAPTER XI.
FLOOD BANKS AND RIVER TRAINING.
If perennial irrigation is given to lands which have hitherto
been subject to inundation from the flood of a river, the crops
that will thereafter be standing on the ground during the flood
season must be secured against submersion by the construction
of protective banks. As the deltas of rivers are formed by the
deposit of recurring floods, the highest land so formed cannot
be above the reach of a maximum flood. Consequently, when
a river delta is brought under perennial irrigation, it is neces-
sary to protect it by making river banks to prevent the floods
from spilling sideways and flowing across country. But the
confinement of the flood discharge to the main channel or
channels of the river is interfering with the natural process
by which the land level has been hitherto gradually raised,
so that henceforward the raising of the land surface will,
if it does not altogether stop, proceed at a much slower
rate than in the past. At the same time the amount of silt
carried by the river and deposited at its mouth, where it
meets the sea, will be at least as much as before, and the
rate at which the river bed will rise in consequence of the
yearly increasing deposit will remain undiminished. The
river bed will, therefore, rise at a more rapid rate than
the land surface alongside it, and with it also the heights
of floods. Consequently it will be found necessary from
time to time to add to the height of the flood protective
embankments, which may thus, after a sufficient period, become
inconveniently high. It has been calculated from the evidence
238 IRRIGATION.
of ancient monuments that the lower portions of the Nile
Valley and its delta have been raised by the natural action of
the river at the rate of 4 inches a century. If, in consequence
of the construction of Nile banks on perennial irrigation being
introduced in the delta, the further raising of the land surface
has been stopped while that of the river bed continues, it will
be found a thousand years hence that the crest of the banks,
if maintained at the same height above highest flood as is the
rule to-dayi will have to be 3 feet 4 inches, or a metre higher
than they are now above mean sea level.
There is another respect in which natural arrangements are
upset by the construction of river protective banks. When
artificial control is absent, the flood in the river branches of a
delta finds its way to the sea not only along the main channels,
but also by spill channels along which part of the river dis-
charge flows at high flood. Below the take-oif of each
successive spill channel there is a decrease in the discharge
which the main channel has to carry. Consequently the dis-
charging capacity of the river channel, which adapts itself to
the work it has to do, constantly diminishes from the head to
the tail. Now, when these spill channels and all side escapes
for the flood water are closed by river protective banks, the
whole flood discharge will flow forwards along the proper
channel of the river; and, since the dimensions of the channel
diminish towards the tail, the flood levels in the lower reaches
will rise higher, relatively to the land alongside the river, than
they did before the spill channels were closed, necessitating the
raising of the flood embankments to contain the floods. This
consideration will affect the question as to how far down the
river branches it is advantageous to extend the river banks and
to prevent the river spilling sideways.
In the delta of Egypt the level of a high flood in one of the
branches is from 3-0 to 3-5 metres (about 10 to 11^ feet) above
country level. These levels are attained in the middle third of
the Damietta branch. At the head of the branch the height of
FLOOD BANKS AND RIVER TRAINING.
239
an extreme flood above country level does not exceed 2 metres
(6J feet). At Damietta, 15 kilometres above the meeting with
the sea, the flood falls to country level. The dimensions,
adopted of late years, for the Nile banks of Lower Egypt are
shown in Fig. 65.
Fig. 65 A gives the section when the high flood level is not
NILE BANKS
more than half a metre above the country level inside the
banks. If the soil is sandy, the crest width is increased to 4
metres. The same crest width of 4 metres is also given to the
bank if it is used as a road.
Fig. 65 B gives the section when the high flood level is over
half a metre but not more than i metre above the country
level. If the bank is used as a road, the crest width is
increased to 5 metres.
240 IRRIGATION.
Fig. 65 C gives the section when the high flood levefl is over
I metre but not more than 2 metres above country level;
and Fig. 65 D when it is over 2 metres above country level.
If infiltration takes place to any considerable extent the
lower slopes of the bank on the land side are made three to one,
or even flatter, as experience may show to be necessary. If the
soil is very sandy, it is better to make the slopes three to one
and to omit the land side berms.
In India, America and, in fact, most countries, the slopes of
the banks are always turfed ; but in Egypt they are left bare,
for the very good reason that there is no grass for turfing to be
found, and there is no rain to keep grass alive if grown from
seed.
In America flood embankments are termed " levees." The
usual dimensions for a levee in the United States are 8 to 10
feet of crest width and slopes of 3 to i. If the soil is sandy the
top width is sometimes made 15 feet and the slopes 5 to i. If
the bank is high, a berm about 20 feet in width is added on the
land side, some 8 feet below the top of the levee, and the slope
of the bank below the berm is made flatter than the slope
above.
In Italy, the Po embankments have a crest wdth of from 23
to 26 feet, sometimes reduced to 16 feet. The side slopes are
formed at 2 to i or 3 to i. There are usually two berms on the
land side.
On the Rhine, the river banks have a top width of only 6 or
7 feet, which is doubled when the crest is utilised as a road.
The slopes are made 3 to i.
In constructing flood embankments the precautions taken to
ensure safety vary considerably in different countries. It is
remarkable what a simple matter the construction of a bank is
in Egypt, and what few precautions are taken. The banks are
thrown up without any special preparation of the land surface
on which they are to be made; the soil is not deposited in
layers, nor watered, nor rammed. The large clods are broken
FLOOD BANKS AND RIVER TRAINING. 24I
up, and the excavation pits are kept at a certain distance from
the outside toes of the finished bank. But this is all. And yet
there is no rain to consolidate the new earthwork, nor is there
turf to protect the slopes. The banks do not breach, at any
rate from the pressure of water. If they did breach for want of
more elaborate methods of construction, more precautionary
measures to obtain security would by now have been introduced.
Probably the dimensions given to the banks in Egypt are
sufficiently liberal to dispense with the methods of construction
which are imperative with banks of comparatively slight
section.
When a breach occurs it is almost always, if not always,
found to be due to causes other than that of direct water-
pressure. Some soils become waterlogged and lose their power
of supporting weight. When this happens below a high bank
subject to a considerable head, the soil supporting it may give
way and cause a subsidence of the bank, sufficient sometimes
to allow the water that is being retained to flow over the top
of the bank and breach it. In such cases it is better to spread
the weight over a broad base by giving the bank flat slopes or
frequent berms, and also to keep the borrow pits at a safe
distance, so that the natural soil may remain intact to resist
settlement.
Sometimes wave action may cause a breach, if a bank is left
at its mercy without protection. But this seldom happens ;
and when it does it is due to negligence on the part of the
watchmen whose duty it is to guard the bank. For the erosion
effected by waves is more or less gradual, and the attack being
made at water surface can be combated and successfully resisted
if adequate means have been provided to meet such a danger.
Light poles, or bamboos, and bundles of long grass or maize
stalks, or any such material that happens to be obtainable in
the neighbourhood, should be collected on the banks before the
flood season, ready for use as required.
A fruitful source of danger is the existence of ill-constructed
I. R
242 IRRIGATION.
culverts made in the banks to irrigate land immediately inside
them. Such works should never be allowed unless they are
built to an approved design and under the supervision of
Government officers or responsible representatives of the
public who are interested in the safety of the banks.
There is one other and more formidable danger to which
river banks are subject. The most frequent cause of breaches
is the undermining action of the flowing river along reaches
where the soil of its margins is light and the velocity of its
current high. If precautions to meet this danger are post-
poned till the flood has come, the chances of successfully
meeting it are slight, except at ruinous expenditure. If the
river embankment is close to the river edge and the river in
flood begins to undermine it, it is often lost labour and
material to throw stone into the deep water, or drive in stakes
along the river front, while the cutting action goes on below
the foot of the stakes. If there is danger of a breach, the only
safe thing to do is to quickly throw up a retired bank at some
distance behind the threatened length, so that it may take up
the duty of protecting the country from inundation in the
event of the original bank being breached. While the safety
bank is being made, the river attack on the original bank must
be held in check and its advance delayed by the best means
available under the particular circumstances of the case.
It is, however, much safer and more economical to anticipate
and guard against the danger of undermining during the low
supply season that precedes the flood. There are two ways of
doing this. The bank may be retired along the threatened
lengths to a safe distance from the river edge beyond the
reach of danger ; or the points and lengths liable to suffer
erosion may be protected by spurs and revetments of sufficient
power of resistance to be relied upon. The latter method is
adopted in the front of villages and wherever a retirement is
impossible or objectionable. Otherwise the former method by
retreat is generally preferable. But better than either method
FLOOD BANKS AND RIVER TRAINING. 243
is a combination of the two. The retirement of the bank from
the river edge to a distance of about 50 yards, and the preven-
tion of further encroachment by the construction of spurs, is
the most satisfactory arrangement. The river bank would
then be safe from any risk of being undermined, and its retire-
ment would not have to be repeated in the future in consequence
of further advances of the river. Spurs as a form of defence
against encroachment are preferable to revetments of the
slope, as they are more efficient and economical, and, when
once established, require less attention than revetments. But
as the eddy created down stream of a spur eats into the bank
for a certain distance, this method cannot be adopted where
the bank to be protected is not sufficiently retired from the
river edge to be outside the limits of the eddy's action. In
such a case the river-side slope rijust be protected by a revet-
ment of stone or other suitable material which will offer
sufficient resistance to prevent encroachment at any point.
The material used in the construction of river spurs and
revetments may be stone, brick, brushwood, or any other
suitable material that may be readily procurable. Stone or
brick has the advantage of durability, and may therefore in the
long run prove to be a more economical material to use than
brushwood.
The forms given to spurs are various. The diversity is due,
probably, to the diff'erent conditions existing at the places
where spurs are found necessary. In India, a form much
favoured is the T form, which has at its outer end a certain
length of spur face parallel to the desired direction of ilow
designed to guide the current. This would be an expensive
arrangement if the spur were to extend into deep water.
In Plate -V. is shown a form of spur existing in Spain. A
timber gridiron, resting against a weighted tripod, forms a
support for the smaller material, such as brushwood, by which
the obstruction to the current is formed.
The usual f jrm of spur adopted in Egypt has its axis inclined
R 2
244 IRRIGATION.
at 120 degrees to the direotion of the current. It has a sloping
crest, commencing at the shore end from a point about 2 feet
above highest flood level, and carried down to a point about
3 feet above low water level at the outer end. The slope of
the crest, therefore, depends upon the length that it may be
decided to give to the spur. Usually it is about 5 to i. The
crest width is made from 3 to 6 feet, and the side and end
slopes are formed at i to i. The spur is connected by an
earthen " tie-back " with the river bank behind it, so that the
flood may not take it in rear. The river side slopes imme-
diately above and below the spur are revetted for short distances
to protect the root of the spur frpm the action of eddies.
Similar spurs are also sometimes made for the protection of
the sides of large canals which at full supply have a discharge
of such volume and velocity that the side slopes suffer from
erosion. Spurs intended for such a purpose are made in pairs,
one spur on either side of the canal, and they are formed with
their axes at right angles to the current. In other respects
thev resemble river spurs, but the position of the outer ends,
and the slope to be given to the crest, are determined by
considerations other than those that apply to river spurs.
When the conditions of soil and discharge are such that the
sides of a canal succumb to erosive action, the eroded material
is carried forward by the water and spread about over the bed"
of the canal further down. Consequently when, as the season
advances, the water level falls with a decreasing discharge, the
obstruction to the flow, caused by the deposits of eroded
material, seriously affects the available water supply. It is
therefore important to prevent such deposits by stopping
erosion. The proper distance apart of the opposing spurs 01
any pair depends on the discharges of the canal, the object
being to produce and maintain a channel of uniform section
and of such dimensions that it will carry its discharge without
any scour or deposit taking place. A practical way of deter-
mining the width of bed to be allowed between the toes of
FLOOD BANKS AND RIVER TRAINING. 245
two opposing spurs is to study a longitudinal section of the
bed made after a flood season, and so to discover the points at
which the bed has remained at the correct level, having been*
neither lowered by scour nor raised by deposit below or above
that level. Cross sections taken at these points will give the
dimensions of the channel, adapted to the conditions of the
canal, which it is desired to determine. The spurs should be
constructed so that the waterway allowed at high flood levels
between the opposing spurs of a pair may approximate to that
of the selected cross sections ; or be a little less, as the velocity
of current must always be accelerated to a certain extent
between the spurs if they perform the work of directing the
flow. The interval between one pair and the next pair of
spurs should be such that the effect of one pair shall begin
where that of the next pair ends. Usually the distance would
be from 200 to 300 yards. Experience of the actual working
of such spurs on the four largest canals in Egypt has demdn-
strated that they are a most efficient means of checking erosion
of the banks and of diminishing thereby the resulting deposits
along the canal bed. The section of the canal is gradually
restored by them to its correct width and depth, and theberms,
which had been cut away, are reformed by a deposit of silt on
the sides of the channel between the pairs of spurs.
River protective works, such as spurs to protect dangerous
points against erosion, are different in their object from river
training works. Canal spurs which are made with the object
of stopping erosion, and also of producing a regular channel of
uniform section, partake of the nature of both protective and
training works. River protective works have usually to b •
made in the deep water which is to be found at threatened
points; river training works are generally carried out in
shallow water. The former, by strength of material, forcibly
prevent the river from injuring its banks; the latter, by gentle
persuasion, induce it to flow in the direction and behave in the
manner desired. '
* See Note 9, Appendix IV.
246 IRRIGATION.
River training works maybe undertaken for different objects.
They may be designed in the interests of irrigation, or of navi-
gation, or for the purpose of reclaiming land ; sometimes also
for the sake of diverting the river channel from a too dangerous
proximity to an important town, building or property of
sufficient value to justify the expense involved.
It is often necessary to train the river for some distance
up stream of the head works of a canal system, in order that
the discharge may flow in a regular channel and correct direc-
tion as it approaches the weir or other river work of regulation.
In India the river Ganges is trained above and below the
Narora weir, at the head of the Lower Ganges canal, for
2ii miles, by works on both banks above the weir and on the
right bank below it. The training works consist of groynes
constructed in pairs at half-mile intervals, each groyne being
tied back to the high ground, canal or parallel bank behind it,
so as to confine the river discharge to the passage between the
heads of the opposing pairs of groynes, and prevent any flow
of flood water behind the groynes. The distance between the
heads of the groynes is 3,000 feet, which is the normal width
of the river. After groynes of various patterns and different
materials had been experimented with, the type eventually
adopted as the most efficient was the T-headed form, and the
material employed was earth with rubble-stone facing and toes.
The cross head of the T groyne was made 400 feet long, with
an up-stream length of 300 feet and a down-stream length of
100 feet. The stalk of the T, or axis of the groyne, was placed
at right angles, and the cross head parallel, to the direction of
flow. Large masses of kankar (nodular limestone) were stacked
on the slopes of the groynes ready to subside into any hole
scoured out below them. The works have been successful in
training the river, but, like most training works, they have been
costly to execute.
The type of spur already described under protective works
as the favoured form in Egypt is made entirely of loose stone,
FLOOD BANKS AND RIVER TRAINING. 247
the tie-back only being of earth. Consequently, if a settlement
at the outer end takes place, it does not necessarily follow that
the consequences are serious. It is in fact expected that newly-
made spurs will settle for two or three years after their con-
struction. If they do, they are repaired and made up to full
section as often as the necessity arises, until at last, as the
result of repeated settlements, the bottom stone reaches such a
low level in the river bed that the scour of the current past the
end of the spur no longer disturbs it, and stability is at length
reached. A spur of this description can also be added to and
lengthened by degrees after it has become established and
stable, so that the effect on the river may be produced by a
gradual process. Powers of persuasion and not of violence
should characterise training works of discretion. Another
virtue that the spur with sloping crest possesses is that the
eddy produced down stream is of comparatively little violence,
as the obstruction is presented to the flow in a gradually
increasing form from the outer toe in deep water to the root of
the spur where it rises above high flood level and unites with
the tie-back.
In Egypt training works have been undertaken at the apex of
the Delta to induce the river to bifurcate at the selected point,
so that the twin channels may flow symmetrically on to the
barrages which span the two branches, and in a direction at
right angles to the face of either work. The training works
consist of spurs to stop any encroachments taking place in a
wrong direction, and to encourage them when they take a right
direction ; of revetments to preserve the river slopes which
coincide with the sides of the ideal channels to be formed ; and
of a bar of anchored mimosa trees, renewed every year, across
the upper end of a side branch of the river which it is desired
should close itself by a deposit of silt.
In Egypt, also, training works have been undertaken by a
company with the object of reclaiming land in the bed of the
river. The works, for the most part, take the form of a
248 IRRIGATION.
regulator at the lower end of a reach, the bed of which is to be
reclaimed. By means of the regulator the flow is checked
during the flood season, so as to produce a velocity most
favourable to the deposition of silt. The bed level is raised by
the deposit of successive floods until it is high enough to be
cultivated. The silting up of side channels, for the object of
reclamation, often effects an improvement in the navigable
conditions of the river.
I The deposition of silt behind spurs takes place more readily
if the spurs are permeable than if they are impermeable. Spurs
made of loose rubble are permeable so long as the interstices
between the stones do not silt up ; and this will only occur
at the same rate at which the silt deposit forms down
stream of the spur, to which there is no objection. Permea-
bility is obtained sometimes by making the spurs of bushy
trees or brushwood ; and, in certain situations, such material is
preferable to stone. But stone is the more durable, and if the
action of the spur is to be continuous and to extend beyond a
period of a few years only, it is to be preferred as the material
of construction ; unless practical considerations, such as the
abundance of other suitable material close at hand, or the
prohibitive cost of stone, call for its rejection. The existence
of abundance of cotton-wood and willows on the Mississippi
river determined the choice of material for the important
training works undertaken in the interests of the navigation of
that river. The aim of the engineers who direct the training
works of the Mississippi is to obtain a uniform channel, and so
to prevent alterations in the velocity of the current, to which is
attributed the mischief of undermining banks and consequent
shoaling. The object is the same as that for which spurs, as
already described, have been made in the large canals of Egypt,
but the means employed are different. The cotton-wood and
willows, woven into mattresses, are sunk in place and fixed
along the sides of the channel to be regularised. For the
protection of banks " mattress revetment is the chief method
\ FLOOD BANKS AND RIVER TRAINING. 249
employed along the Mississippi and Missouri rivers. The brush
grows in abundance, and in spite of continued denudation for
these worts the supply has not been exhausted, as cotton-wood
and willows spring up rapidly, so that it is the cheapest
material for use. Out of the abundance and cheapness of this
material has grown the practice of its use, in connection with
stone, also fairly plentiful, as a revetment for banks in this
country (U. S. America)."'
1 " The Improvement of Rivers," by B. f . Thomas and D. A. Watt.
CHAPTER XII.
/
AGRICULTURAL OPERATIONS AND RECLAMATION WORKS.
It has already been shown in Chapter III. that an irrigation
engineer must acquire a correct knowledge of certain agricul-
tural matters before he can estimate with any confidence the
quantity of water that the canals will have to carry at different
seasons. In fact the more complete his knowledge of such
matters, the more competent will he be to design a project
adapted to the needs of the land to be irrigated. The configura-
tion of the ground, the nature of the soil, the description of the
crops, the seasons of sowing and harvest, the times when water
is needed, the habits of the cultivators, must all be considered
when the " duty" of water for the prospective canal system is
being determined. Again, when the financial results of any irriga-
tion scheme are being calculated, it is not enough to include on
the expenditure side the cost only of the canal and drainage
works ; but an allowance must be made for the sometimes
considerable expense that the landowner will incur in preparing
the ground for the application of irrigation. The ground may
have to be levelled, or to be cleared of scrub or other growth ;
but, in any case, field channels, or ridges to divide the area into
compartments or terraces for flooding, or other means for the
internal distribution of the water, must be provided. The cost
of these private operations will naturally vary with the condi-
tions. M. Salvador, in his St. Louis paper on " Irrigation in
France," states that it may be estimated at from 500 to 800
francs per hectare (£"8 to £13 per acre). This estimate will
appear exaggerated to those whose experience has been gained
in countries where the agricultural conditions are peculiarly
AGRICULTURAL OPERATIONS AND RECLAMATION WORKS. 251
favourable to irrigation, but those whose experience is of opposite
conditions may reckon this estimate to be moderate.
In the preliminary stages of a project, information concerning
the needs of agriculture, so far as irrigation is concerned, will
be sought after by consulting the local farmers. But it must
not be assumed that the cultivator's judgment as to what is best
for his crops is infallible, when the conditions of farming,
introduced by irrigation, are outside the limits of his experience.
When the quantity of water obtainable is abundant and the
farmer does not pay for it according to the actual quantity
taken, he is apt to over-water his crop, and has to be taught by
experience that, though water is a good thing, a crop may have
too much of it. Especially is this the case if a deficiency in
the supply of water has been the normal condition under which
crops have had to be raised previous to the introduction of
irrigation. Cotton cultivation, for instance, appears to suffer
from a too liberal supply of water. It was said some years
ago, with reference to the cotton crop in Egypt, that the
shorter the water supply the greater the yield of the crop.
This generalisation, based on the figures of a few years only,
could obviously be discredited by a reductio ad adsurdum. But
the figures of the cotton crop of Egypt for late years seem to
show that over-watering is practised when the opportunity
offers, and that over-watering is followed by a decrease in yield.
The total yield for all Egypt in 1897 was 6,513,444 cwt.; in
1899, 6,432,776 ; in 1901, 6,369,911. For the intermediate years
it was less. In 1903 the Assuan reservoir was filled and drawn
upon for the first time, and there was a considerable extension
of the area put under cotton in 1903 and 1904. Nevertheless,
in both those years the yield was less than it had been before
1903. There was no advance on the record figure of 1897 in
spite of the extension of the area under crop. The of&cial
reports of the Irrigation Department of Eg57pt state that the
water supply of 1903 and 1904 " was everywhere plentiful ; too
plentiful perhaps." It is possible that, as the area increases
252 IRRIGATION.
under the stimulus of the increased supply and the water allow-
ance per acre becomes less, the yield per acre may again rise to
as high a figure as it had reached before the Assuan dam came
into operation. If so, the record total yield of Egypt of
1897 will then be surpassed by a considerable figure. Now, in
the Irrigation Report for 1904, it is stated that the " duty "
that was got out of the water in the summer of 1904 was
" probably the lowest ever recorded," and that there had not
been such a good summer supply in the river since 1899. The
moral of this would seem to be that, if a given quantity of
water is best suited to any crop, it is a mistake to give more
than that quantity ; and the irrigation officers would be acting
in the interests of the farmers if they were to make excessive
watering impossible by withholding the super-abundant supply,
even if so doing necessitated running water to waste.i But to
run water to waste when cultivators are demanding more, even
though giving way to the demand would be prejudicial to their
interests, is an unpopular thing to do, and is a difficult policy
to carry out in the face of an almost universal belief that, in a
conflict of opinions between the irrigation officer and the
agriculturist over a question concerning crop requirements, the
former must necessarily be in the wrong. A good irrigation
engineer will be all the better for a sound knowledge of the
agricultural conditions and needs of the district which is or will
be affected by the canal system under his control, and it is part
of his duty to acquire such knowledge, so as to enable him
to apply his professional ability to the best advantage.
The limitation of the water supply, in a healthy system of
canals, to the real requirements of the crops, has a further
advantage beyond the prevention of over-watering. It also pro-
tects the drains, which have to carry off the excess, from being
over- worked to such an extent that they cannot perform their
part efficiently. When the excess that reaches them is reason-
able in quantity and no more than they have been designed to
* See Note 10, Appendix IV.
AGRICULTURAL OPERATIONS AND RECLAMATION WORKS. 253
carry off, the evils of water-logging and stagnation are avoided.
It has been said that irrigation water, to be entirely beneficial,
must reach everywhere, but remain nowhere. The putting into
practice of this theoretical formula is most difficult in the case
of the low-lying lands of flat slope which lie along the sea-ward
margin of most deltas. Such lands are often salted, and the
problem of their reclamation is, therefore, not solved by merely
getting rid of the water that covers them permanently or occa-
sionally, and by draining them ; but the salt that makes the
land infertile must be washed out of it. The land surface is so
little above sea-level that drainage by gravitation, or free flow,
is an impossibility. The water has to be got rid of by pumping.
There are wide stretches of low-l5dng level lands, at present
barren wastes and marshes, lying unreclaimed along the north
margin of the delta of Egypt. There is so much else in Egypt
that it pays better to reclaim or develop, that it will be many
years yet before cultivation extends northwards from its present
limit as far as the borders of the sea.
The reclamation of such lands, however, is a possibility.
Holland, and the valley of the Po in Italy, furnish instances of
successful reclamation. The first thing to do is to get rid of
the salt in the soil. If the flood water of the river can be made
to flow fi-eely over the surface, some of the salt will be carried
away in the water. But it is not often possible to secure surface
washings sufficiently copious or prolonged to remove the salt
for more than a comparatively shallow depth. The salt below
is more efifectually got rid of by a system of deep drains into
which the water finds its way by downward percolation through
the soil, carrying the salt with it. These operations of surface
washings and subsoil drainage can be effected in the following
way. The land to be reclaimed would be surrounded by a
bank to exclude all water other than that purposely admitted.
The earth to form the bank would be obtained from a ditch
dug along the inside of it to a regular section to serve as a
collecting drain. At the higher end of this enclosure, at the most
254 IRRIOATION.
convenient point, a head sluice on tRe feeder canal would admit
water under control. At either end of the lower side escapes
would provide exits for the water of surface washings. At the
lowest point of the enclosure, or at the most convenient point
on the interior drain, a pump to lift the drainage water would
be set up. Irrigating channels in connection with the head
sluice would distribute the water admitted over the enclosed
area, and drains, alternating with the irrigating channels, would
lead to the pumping station. The first operation of surface
washing would then be conducted, during the season when
water was plentiful, by opening the head-sluice and keeping the
escapes closed until the whole of the enclosed area was covered
with a sheet of water. As soon as that had occurred, the
escapes would be opened to the extent necessary to discharge as
much as was being admitted through the head sluice, so that
the water level in the enclosure might remain constant. When
it was no longer possible to continue the supply, the head sluice
would be closed, the escapes be fully opened, and the water run
off to as low a level as it would go. When it ceased to flow, the
escapes would be closed to prevent a back flow, and the pumps
would hft the remaining water into a discharging channel outside
the enclosure, which would carry it away. The drain along the
inside of the enclosing bank and the drains all over the area, alter-
nating with irrigating channels, would lead all excess water to
the pumping station and keep the saturation level low. The head-
sluice would admit the supply required for the irrigation of the
crops or for other operations, and the irrigation channels would,
distribute it. The surface washing would probably have to be
repeated more than once before the soil would become cultivable.
But meanwhile, after a surface washing, supposing water is
available, the system of subsoil drainage would be brought'
into play to do its part in getting rid of the salt. The method
of proceeding consists in surrounding plots of land of con-
venient dimensions by ridges, and filling the enclosed plotswith
water of, say, one foot in depth. The water in the deep drams
AGRICULTURAL OPERATIONS AND RECLAMATION WORKS. 255
alongside the plots is kept low by the pumps. The watei
covering the plots sinks into the ground and percolates down-
wards and outwards to the drains, carrying salt with it. The
plots are filled again and again, and the process repeated till the
soil is sufficiently free of salt to be cultivable.
Finally, to enrich the soil, the turbid flood water should be
admitted and kept standing in the enclosed area long enough
to throw down its fertilising matter, and be then run off. It is
well to make provision, in the arrangements for the reclamation
of these low lands, for periodical washings every third year or
so, as their tendency is to return to their original salted con-
dition ; and it is therefore necessary to adopt effective measures
to counteract the tendency.
Whether it is worth while to incur the expenditure of reclaim-
ing land which, it might be urged. Nature has not intended for
cultivation, depends upon many things. It has been argued
that, inasmuch as it pays to lift water for raising crops by
irrigation on high lands which get free flow drainage, it should
pay to bring land under cultivation by lifting the drainage water
that runs off land which enjoys free flow irrigation, because the
amount drained off irrigated land must of necessity be less than
the amount supplied for its irrigation. This argument would be
conclusive if the yield of the crops in both cases were the same.
But that is often by no means the case, the low lands after
reclamation being generally poor in quality in comparison with
the high lands. In Egypt the high lands near the head of the
delta, for the irrigation of which water has to be pumped, yield
twice as much cotton per acre as the low lands in the north of
the delta near the sea.
There is another difficulty which must not be lost sight of in
considering the pros and cons, of any reclamation scheme. There
would generally be a want of hands to carry out the operations
of reclamation and farming, as no villages or habitations would
be found on waste lands that produce nothing. The population
would have to be brought from elsewhere and given inducements
2S6 IRRIGATION,
to settle. Means of transport would also have to be provided
for the conveyance of the produce of the land to a market where
it could be sold. In Chapter I. it has already been told how, in
India, a new population of 1,000,000 founded homesteads on
some 2,000,000 acres of waste land which had been reclaimed to
cultivation by the waters of the Lower Chenab Canal. But it is
not all countries that have such human reserves as India has to
draw upon ; and want of population will often necessitate the
postponement of reclamation schemes.
Another important consideration in estimating the financial
prospects of any scheme involving pumping on any considerable
scale is the cost of the fuel required for generating power by
steam, electricity or other means, whether the object is irrigation
or drainage. For fuel is the most important item in the pump-
ing expenditure. Large pumping stations work more economi-
cally than small ones, the establishment and other charges being
relatively less in a large than in a small installation. There is a
large pumping station at Mex (Plate IX.>, near Alexandria, which
works in the interests of drainage. A large area of the western
deha of Egypt drains into Lake Mareotis, and the efficiency of
the drains depends on the control of the surface level of the lake.
It is the business of the Mex pumps, therefore, to keep the lake
surface from rising above a certain fixed level. The pumping
station consists of two 48 inch centrifugals with horizontal shafts,
and 5 centrifugals with vertical shafts (shown under erection in
PlatelX.) worked byseven engines of anaggregateof 1,500 w.h.p.
It is capable of lifting a maximum of 35 cubic metres (1,227
cubic feet) per second. In 1918 the pumps, working for
286 days, lifted 624,000,000 cubic metres of water at a total
cost of about £50,000. The price of fuel was in that year
abnormally high on account of the war.
A much smaller pumping station at Kassassin, also for
drainage purposes, Ufts water 2 J to 3 metres. In 1918 the cost
of the pumping was at the rate of nearly £200 per milUon cubic
metres — an abnormal rate, due to war conditions. This
AGRICULTURAL OPERATIONS AND RECLAMATION WORKS. 2S7
station is capable of lifting sf cubic metres (about 200 cubic
feet) a second. It is composed of five engines driving six
centrifugal pumps with horizontal shafts. With smaller
stations the cost per unit of volume pumped would be consider-
ably higher. Sir William Willcocks, nevertheless, recommends
small pumping stations in the case of reclamation work. In
his lecture on Irrigation on the Tigris, delivered in Cairo on
March 25th, 1903, he expresses his opinion in the following
words- — "The important point is, that numbers of small pumps
should be placed on the banks of the main drains, draining
small areas and discharging direct into the mains. Such
pumps should be actuated by one central electric station for
reasons of economy. The results of such drainage would be
immediately apparent. The early failures of large reclamation
works were nearly always due to the extensive areas drained by
single installations." He considers the most economical area
to drain with one pump to be 2,500 acres.
The new departure of the Irrigation Service of India in adopt-
ing a pumping scheme for the irrigation of the Divi Island, on
the Kistna river in Madras, has already been referred to at tne
end of Chapter VI. As was there stated, the pumping station
consists of eight i6o-brake-horse-power Diesel oil engines, each
actuating a Gwynne centrifugal pump with a 39-inch diameter
discharge pipe. The pumps lift water 10 to 12 feet for the
irrigation- of 50,000 acres. The estimated cost of the first
installation was, in roi*ad figures, £35.ooo- The quantity of
water lifted is 500 cubic feet a second. The fuel used is oil.
The estimated annual expenditure, with a pumping season of
4 months continuous work hfting 500 cubic feet a second, was
£7,384 for a total quantity hfted of 5,184,000,000 cubic feet.
This gives a rate of £1 8s. 6d. per 1,000,000 cubic feet, or £50 per
1,000,000 cubic metres, hfted.^
1 The Government of India Report for 1916-17 states; "Although it has
only been completed for somewhat over thr?e years, a net return upon capital
of 3j per cent, is already being realised."
I. s
CHAPTER XIII.
NAVIGATION.
The waterway provided by the construction of an irrigation
canal is often adapted to navigation. Whether it is desirable
to make one and the same canal serve two masters is a question
that has been much disputed by the canal engineers of India,
ever since Sir Arthur Cotton, in 1854, preached the gospel of
navigation. The question does not seem to be finally settled
yet. It is probable that the combination of irrigation and
navigation is desirable in some cases and not in others, but
that it is not so generally desirable as the early enthusiasts for
navigation asserted. In a paper on the Navigable Waterways
of India, read on Feb. 15th, 1906, before the Indian Section of
the Society of Arts by Mr. R. B. Buckley, C.S.I., it was shown
that, out of a total length of 11,858 miles of irrigation canals,
in India, 2,778 miles were navigable. Judged by the receipts
credited under the head of navigation, it cannot be said that, as
a rule, there has been a satisfactory return for the expenditure
incurred in adapting irrigation canals to navigation. Mr.
Buckley mentions the Godavery system in Madras, and the
Orissa and Midnapore systems in Bengal, as the canals in
which navigation has been most successfully combined with
irrigation.
An irrigation canal should follow the line which is best
suited to it as an irrigating channel ; a navigation canal should
connect the producing areas with the markets, where the
products are to be disposed of, by the most direct line that may
be economically possible. It is not likely that the two lines
would be identical, though occasionally they might ba I^
NAVIGATION. 259
irrigation and navigation are to be partners in one business
there must be compromises arranged, since what is best for the
one is not so for the other. The principles on which an
irrigation canal should be designed have been pointed out in
Chapter VIII. It was shown that the velocity of flow should
be such that there would be neither deposit of silt nor scour of
the bed or banks. A velocity complying with these conditions
might very easily be too high for the convenience of naviga-
tion, which would be better suited by a sluggish current or no
current at all. It has also been explained in Chapter X. that it
is desirable for economical distribution of water in irrigation to
regulate the discharges in the canals so that periods of low
supply should alternate with periods of high supply. Such a
fluctuating system would be very disconcerting to boats, at any
rate when fully laden. There are besides other respects in
which irrigation and navigation requirements conflict when the
same canal has to satisfy both. Nevertheless it is sometimes
advantageous, all things considered, to make' an irrigation canal
navigable, so that it may not only furnish the means for raising
products of the soil, but may also offer facilities for transporting
the same products to market. The importance of inland
waterways as affording a cheap method of transport for bulky
goods of all descriptions has received practical recognition in
France, Belgium, Germany and America to the great advantage
of their trade. But the canals which form part of their
schemes of inland waterways are, for the most part, designed
exclusively for navigation purposes, and are unconnected with
irrigation. It is in India and Egypt that examples of canals
serving both objects will be found.
A navigable canal, or navigable system of canals, must, in
the first place, have uniformity of gauge, that is, the locks
should all have the same dimensions and the canals an uniform
cross section, so that the largest sized craft that can navigate
any part of the system can navigate it throughout.
When an irrigation canal has to be adapted 10 navigation, it
S 2
260 IRRIGATION,
is necessary to reduce the velocity of flow so that it may not
exceed from i^ to 2 feet a second. As in most cases, when
this condition is compHed with, the water-surface slope of the
canal will be jess than that of the land surface, it will be
necessary to provide falls at intervals along the canal, so that
when the water level has reached the maximum height above
country level that is convenient, it may be dropped down
within soil. At each point where a fall is necessary, a lock
must be built to give passage to boats between the upper and
lower reaches.
There are three different positions in which the lock may be
placed with reference to the fall with which it is associated.
The fall may be placed on the main canal, and the lock on
a side channel taking off from the canal above the fall and
rejoining it below. Or the lock may be on a navigable channel
dug on the direct line of the canal axis, while the fall is placed
on the main channel which is diverted round the lock on a
curved alignment. In both these cases the fall and lock are
usually built in such positions that the roadway over the two may
be in one straight line. The third plan is to make a combined
work of lock and fall, and to have no side channel. The
advantage of the last arrangement is that the entrance to the
lock is kept clear of silt ; the disadvantage is, that when the
discharge over the fall is considerable, the draw of the current
may make it difficult, or even dangerous, for boats to enter the
lock. On the other hand, the disadvantage of placing the lock
on a separate channel from the fall is that the channel above
and below the lock has a tendency to silt up, and, if not kept
clear by dredging or otherwise, boats may find it not merely
difficult, but impossible to enter the lock. But a lock so
placed has the advantage that the entrance and exit of boats
is effected in still water.
Sometimes, instead of a fall or weir to hold up the water
with the object of reducing the velocity of flow or of producing
a sufficient depth for boats in the reach above, a regulator is
NAVIGATION. 26 1
necessary for the purpose of raising or lowering the water level
to suit the needs of irrigation. Whenever the regulator may
be used to hold the water in the upper reach at a higher level
than that in the lower reach, the lock comes into action for the
passage of boats ; but when the regulator is fully open, both
pairs of lock gates also can be opened, and boats be passed
freely without the necessity of bringing the locking arrangements
into operation.
The chamber of a lock may be looked upon as a very short
reach of canal with regulators at the upper and lower ends, by
means of which the water level between them can be raised
and lowered at will to the levels of the reaches above and
below respectively, so that boats may be raised or lowered
from one to the other. The pairs of lock gates with their face
sluices, and the filling and emptying side sluices, perform the
office of regulators. In fact, it sometimes happens that a
reach of a canal is treated as a lock. If the discharge of an
irrigation canal, which is navigable, falls below the normal
minimum contemplated when grading the canal, or if the bed
is raised by silt deposit, boats often run aground at the upper
end of a reach, or in the down-stream exit channel of the lock,
and are either unable to enter the lock if ascending the canal,
or to leave the lock if descending. It then becomes necessary
to hold up the water by regulation at the lower end of the reach,
so that there may be depth of water enough for boats to pass
in and out of the lock at the upper end of the reach. A very
large lock might be economically made on a canal by separating
the two pairs of gates and their sluices into^two distinct works
with the chamber between them formed by a convenient length
of the earthen channel of the canal. In harbours the lock
chamber is sometimes developed into a basin of considerable
area. But the dimensions of canal lock chambers are limited
for reasons other than economy of construction. Economy of
water in the working of a canal is often a more important
consideration than economy in the first cost of construction.
262 IRRIGATION.
Every time boats are passed through a lock, a volume of water
equal to that required to raise the level in the lock chamber
from that of the lower to the higher reach has to be passed
forward from above to below the lock. In irrigation canals — in
their upper reaches at any rate — this is not a serious matter, as
the passing forward of water is always required to feed the
distributing canals. But in purely navigation canals, where
the supply of water for keeping the reaches full is extremely
limited, economy of the available water supply may become a
question of first importance, calling for devices such as lifts
and inclines to promote economy. Another matter affecting
the dimensions of lock chambers is the value of time. Given
the same discharging capacity of sluices, a large lock naturally
takes longer to fill than a small one, and the time taken by the
canal traffic to pass from one reach to the other would be
greater with the large lock ; and unnecessarily greater, whenever
the lock space is only partially utilised by passing boats or
barges. The dimensions of the lock should therefore be deta:-
mined by the traffic which may be expected to use the canal,
and should not be excessive.
The most common form of lock gates is that in which a pair
of gates meet at an angle and are pressed against each other
and against a bed sill by the head of water bearing against
them. The gates may be of wood or iron, and the sill faces of
wood, iron or masonry ; but wood is not used in important
locks. ^ A less common form is the single leaf gate, which spans
the lock chamber from side to side and bears against vertical
faces in the sides of the lock. To open the lock, the gate is
withdrawn sideways into a recess buiit at right angles to the
lock chamber. In the locks of the Assuan dam such a single
leaf gate has been the form adopted. It is hung from above by
seven pairs of sling rods, attached to two sets of free rollers,
which are free to move along two bascule girders spanning the
lock. The gate is withdrawn into a recess in the side of the lock
by the movement of its supporting rollers along the bascule
NAVIGATION. 263
girder. When the gate is safely housed in its recess beyond
the pivoting end of the bascule girder, the latter is raised into
a vertical position to free the passage way for vessels using the
lock. The opening and closing of the valves of the lock gates,
the moving of the gate backwards and forwards, and the lifting
of the bascule girder, are all effected by hydraulic power. The
system adopted at Assuan has proved expensive, and is not
likely to be imitated for gates of smaller dimensions than those
of the Assuan dam locks.
In some cases the single leaf gate, instead of being suspended
from above, rests upon the floor of the lock ; and, to facilitate
its movement backwards and forwards from and to the recess,
arrangements are made for floating it.
A lock has, in certain situations, to be furnished with gates to
act when the normal head is reversed. Such conditions would
exist where a lock constituted the connecting work between
the terminal reach of a canal and a tidal harbour. In such a
case the gates would have to be duplicated, so that the levels
in the lock might be controlled on whichever side the higher
water might be.
As time is often a serious consideration in the transport of
goods, and as every lock on a navigable line is a source of
delay, it is important to arrange for passing boats through
locks as quickly as possible. To this end means must be pro-
vided for rapidly filling and emptying the lock chamber. The
Manual on Irrigation Works of the College of Engineering in
Madras lays it down that " locks should be capable of being
filled or emptied in three minutes." The filling and emptying
is effected by sluices in the lock gates, often assisted by sluice
ways built round the gates in the thickness of the lock walls.
The discharging capacity of the sluices must be sufficient to
effect the filling or emptying of the lock within the maximum
period permissible. The filling sluice-way in the lock walls is
sometimes carried along the whole length of the chamber, and
is given several outlets into it at intervals along its length with
264 mUlGATlON.
the object of diminishing the back-waters and eddies which
are produced, to the inconvenience and sometimes danger of
boats, when the inflow is concentrated at one or two points
only.
But the most important matter affecting the disposition of
the sluices is the tendency of silt to deposit against the up-
stream face of the gates, creating thereby an impediment to
their opening. To counteract this tendency, sluices are fitted
in the face of the lock gates at as low a level as the design of
the gates permits. The inlets of the side sluices in the masonry
of the lock walls are also so disposed as to create a scouring
action over the floor immediately up stream of the gates. In
the case of a lock fitted with the ordinary pair of gates meeting
at an angle, the inlet openings to the sluice way are made in
the face of the recess in which the gate lies when fully open ;
and their sills are placed on a level with the floor over which
the gates move. In the Zifta barrage lock there are three
such inlets in each gate recess communicating with one united
sluiceway, which in the case of the upper gate sluices (Fig. 66)
leads to an outlet into the lock chamber, and in the case of the
lower gate sluices into the channel below the lock. Difficulties
arising from silt deposit above and within locks are especially
met with in the case of locks at the off-take of a canal from a
muddy river, and on irrigation canals adapted to navigation,
which carry silt laden water for the sake of the cultivation
served by them. An intelligent and experienced lock-keeper
in charge of a lock with well designed sluices can do much,
by a skilful manipulation of the sluice gates, to minimise the
inconveniences arising from silt deposit.
The chamber walls of a lock when empty act as retaining
walls to support the earth backing. The dimensions, however,
of an ordinary retaining wall are considered insufficient for a
lock wall, as the rapid emptying of the lock chamber brings
pressures to bear on the wall which are somewhat in the nature
of those due to a live load. If the wall has an interior vertical
NAVlGAtlON.
265
face, a thickness of 3 feet at the top, and a hack batter of i in
4 obtained by offsets, will give a profile that is suitable in most
cases. The Zifta barrage lock (Fig. 67) furnishes an example
of a lock with interior vertical faces ; the Assuan lock (Fig. 68)
that of a lock having interior faces built with a batter. Though
the latter gives a better disposition of the material for resisting
the pressure of the backing, there is, in some cases, a serious
objection to diminishing the width of the lock chamber between
high water and low water levels. For if, when the water in a
ZIFTA BARRAGE LOCK
' 059
ItTtT-
Scale
50
I I I
I I I
100
Z^ Feet
FiQ 66
FIG 67
PUAN OF SIDE SLUICES
)STR
^£f^-^az!jfli;;
GATS
RXCSSS
sipg sttrrcxs -—
-v
09
m
O
k O
m- ■■* o
>
03
a a. Udells of Sluice Gates
OJ
lock with interior face batter is at the level of the upper reach,
boats are admitted in such numbers that they completely fill the
lock from side to side, they will do more than fill it when the
water is lowered, and may be capsized by one side being held
up against the lock wall while the other sinks with the water.
As a rule, from 15 to 16 feet is about the maximum difference
of level that is overcome by one lock. If the difference is
greater, the change of level is effected by two locks, a double
lock, or a flight or ladder of locks. The total drop at the
Assuan dam, from the high water level in the reservoir above
the dam to the river low water level below it, is 90 feet. To
266
IRRIGATION.
'pass boats, a five-fold flight of locks has been provided on one
flank of the dam.
It is a not uncommon thing for a longitudinal crack to
appear in the floor of a lock under construction, when the walls
have reached a certain height. This occurs when the soil on
which the lock is built is compressible, and the pressure over
UPSTREAM LOCK ASSUAN DAM
tllllllMiT
Scale
Feet
FIQ 68
ROCK
the area of the foundations is unequally distributed, producing
uneven settlement. If the centre of pressure of the weight of
the wall and its earth backing falls so far behind the centre
of the figure of the base as to be beyond the safe limit, the
inequality that produces settlement is established. But this
result can be avoided by giving the base a considerable width
and lightening the back of the walls by a distribution of void
spaces in the thickness of the masonry.
APPENDIX I.
WEIGHTS AND MEASURES.
Weights. i
I cubic foot of water weighs 6ai lbs.
1 cubic metre of water weiglis i ton (very nearly).
I kilogramme = 2-2046 lbs.
I lb. = "4536 kilogramme.
I lb. per square inch = '0703 kilogramme per square centimetre.
I kilogramme per square centimetre = 14-22 lbs. per square iucn
Lineal Measures.
I metre = 3-2809 feet.
I foot =-3048 metre.
5 miles = 8 kilometres (approx,).
Square Measures.
1 square metre = io'7643 square feet.
I square foot = -0929 square metre.
I acre = 4046-71 square metres.
I feddan = 4200-S3 square metres.
1 feddan = 1-038 acres.
1 hectare = 10,000 square metrtsa.
I hectare = 2-4711 acres.
I square mile = 640 acres.
I square mile = 27,878,400 square feet.
1 square kilometre = 100 hectares.
I square kilometre = 247 acres.
Cubic Measures.
I cubic foot = 6-2355 gallons.
I cubic foot = 28-3 litres.
I cubic foot = -028315 cubic metre.
I cubic metre = 35-3166 cubic feet.
I cubic metre = 61,028 cubic inches.
I litre = 61 -02 cubic inches.
1 litre = -0353 cubic feet.
26^8 APPENDIX.
1 litre = "32 gallon.
I litre = '88 quart.
I litre = 176 pint.
I cubic metre = 220'og7 gallons.
I gallon = "004543 cubic metre.
I acre foot = 43,560 cubic feet.
I acre foot = i233"4 cubic metres.
1,000,000 cubic feet = 43 acre feet (approx.).
Discharge Measures.
I cubic foot a second is sometimes abbreviated to
I cusec in India, and to
I second foot in America.
I second foot = 50 California, Nevada, Idaho, or Utah inches
I second foot = 38*4 Colorado inches.
1 cubip foot a second amounts to 86,400 cubic feet a day, or 2,445 cubic
metres a day.
1,000,000 cubic metres a day is given by a discharge of ii"574i cubic
metres a second, or 409 cubic feet a second.
I cubic loot a second for 30 days gives 59J acre feet.
I cubic foot a second for 24 hours gives 2 acre feet (approx.).
100 California Laches for 24 hours gives 4 acre feet.
100 Colorado inches for 24 hours gives 5i acre feet.
1 acre foot is given by 25*2 California inches in 24 hours.
Duty of Water.
Equivalent Expressions.
I cubic foot a second per 100 acres gives the same allowance as
I cubic metre a second per 1430 hectares, or i cubic metre a second per
3402 feddans, or 25*4 cubic metres a day for each feddan.
I litre per second per hectare gives the same allowance ol water as
I cubic foot per second per 70 acres.
APPENDIX II.
FORMULAS AND DISCHARGE MEASUREMENTS.
The formulas in most common use by irrigation engineers are those
which relate to the flow of water in open cbanneis , to discharges over
weirs, both clear overfall and submerged ; and to discharges through the
vents of canal or river regulators, lock sluices and syphon barrels.
Tiie fundamental formulas on which the whole science of hydraulics is
based are three, namely : —
Formula (i). Q = A X V.
Formula (2). V = c V ■z g H.
Formula (3). V = e V RS.
The symbols contained in these formulas have the following
significations : —
A is the area of any section of discharging waterway,
V is the mean velocity of that section.
Q is the discharge.
g is gravity acceleration.
H is the head of water.
c is a co-efficient (given in Tables) depending on the nature and
condition of the discharging waterway.
R is the hydraulic mean depth or mean radius ; its value is obtained by
dividing the area of the water cross section by its wetted perimeter.
S is the hydraulic slope or sine of the inclination of the water surface,
or, in other words, the fall of water surface per unit of length of
channel.
Formula (i) is applicable in all cases ; Formula (3) is applicable to open
channels ; Formula (2) to sluice ways.
The formulas for weir discharges are deduced from Formula (2). That
for a clear overfall weir, without velocity of approach, is
Formula (4). Q = § c X A Vzgh
in which h is the depth of water on the weir sill. In this case A = the
length of the weir crest X /.
270
APPENDIX.
The formula for a submerged weir, without velocity of apgroach, is
Formula (5). Q = c X / VT^{di + f di).
in which { is the length of the weir crest,
di is the difference of level between the water surfaces up stream
and down stream of the weir,
and da is the depth of the sill crest below the down-stream water
surface.
If there is velocity of approach, as is usually the case with canal falls,
allowance has to be made for it. The head of water which would produce
the known velocity of approach must be calculated from Formula (a) —
V = c V2 ffH — and be added to the head of water in Formulas (4) and (5).
In Formula (4) it is added to h, in Formula (5) to di.
The value of gravity acceleration g varies in different parts of the world,
from 32"z5 to sa'og feet per second : but it is usually taken as 33"3 feet per
second ; and that is the figure to substitute for g in the formulas when
English measures are used. But if metric measures are used, g ^= g'&i,
the equivalent for 32*2 feet a second. Confusion will result, when using
the formulas containing g, if a change is made from one system of measures
to another and this alteration of the numerical value of g is forgotten.
The value of the co-efficient c is given in Tables for different values
of R, the hydraulic mean depth. But here again, the value of c changes
with change of measures employed, and separate Tables of Values for c
are required for R in feet and R in metres. Bazin's Values have, perhaps,
been more generally accepted than others by hydraulic engineers, and are,
therefore, here given — Table I. for use with English measures, and
Table II. for use with metric measures : —
TABLE I.
Bazin's Values of c in the Formula V =
English Measures.
: c J RS FOR use with
H^drsiulic Mean
Material of Bed and Sides of Cliannel.
Depth.
R in Feet.
Plastered.
Planed Planks.
Dressed Stone.
Brickwork.
Rubble Masonry.
Earth.
•85
125-4
94-8
56-5
25-9
•50
135-3
I08-8
73-0
35-7
•75
139-1
ii5'0
80-8
43-6
I'OO
I4I-3
118-5
867
47-9
1-25
142-4
iao-8
go-g
52-3
i-So
143-3
133*4
94-0
56-0
175
143-9
133-6
965
59-2
a-oo
144-4
124-5
985
63-0
3-50
145- 1
125-8
101-5
66-6
3-00
145-6
126-7
103-6
70-4
3-50
145-9
137-3
105-3
73-5
400
146-1
187-8
1065
76-1
5-00
146-5
128-5
108-a
8o-a
6-00
147
139
110
834
APPENDIX.
271
TABLE I. — continued.
HydiauUo Mean
Material of Bed and Sides of Channel.
Depth.
R in Feet.
Plastered.
Planed Planks.
Dressed Stone.
Brickwork.
Rubble Masonry,
Earth.
7"0O
8-0O
I0"00
la-oo
1500
ao-oo
40'oo
70*00
lOO'OO
Inf.
147
147
147
147
H7
148
148
148
148
148
139
130
130
130
130
131
131
131
131
131
110
III
iia
"3
114
115
116
116
116
117
86-0
88-0
9J"a
93'4
959
98-6
103-1
105a
io6-i
108-3
TABLE II.
Bazin's Valdes of c in the Formula V = c J 'RS for use with
Metric Measures.
Material of Bed and Sides of Channel,
Hydraulic Mean
Depth.
R in Metres.
Plastered.
Planed Planks.
Dressed Stone.
Brickwork.
Rubble Masonry,
Earth.
0-05
65
47
26
,^__
O'lO
72
56
35
16
0-15
73
60
40
20
0-20
76
6a
43
33
0-25
77
64
46
24
030
78
65
48
26
0-35
78
66
49
38
0-40
79
67
51
29
0-50
79
68
53
33
o-6o
L°
69
54
34
0-70
69
55
36
o-8o
80
70
56
37
I -00
80
70
58
40
1-50
81
71
60
44
a-oo
81
71
61
47
3-50
81
72
61
49
3"oo
81
72
6a
50
4-00
81
73
63
5a
5-00
81
73
63
54
1000
81
78 .
64
56
15-00
81
73 '
64
57
The above Tables of values for c takes into account the roughness of the
bed and the hydraulic mean depth, but not the hydraulic slope, which in
extreme oases has to be considered. In all ordinary canals and rivers the
272
APPENDIX.
value of c is not affected by the slope. But in mountain torrents and in
channels with a very gentle surface slope, such as the tail reaches of rivers
near the sea, the hydraulic slope is a factor to be taken into account for
determining the correct value of c. The formula, known as Ganguillet
and Kutter's, embraces this consideration, the value of c in the formula,
V = c V R S, being represented by the expression
I , m
« + V + -5
in which n is the coefficient of roughness depending on the nature of the
surface of the channel, and a, I and m are constants derived from
experiment, the other letters having the same signification as in
Formula (3) above.
When the values of the symbols in the formula are expressed in English
feet, a, I, and m have the following values :—
a = 41 '6604676.
/ = I-8II3350.
m = 0-0028075.
When metrical measures are used,
a = 23.
/ = I.
w= -ooiss.
n has the following values for channels of different surfaces : —
Values of n.
n = -013
n = -017
n == "025
■035
Nature and Material of Channel.
Plaster in pure cement : planed timber : glazed, coated
or enamelled stoneware and iron pipes : glazed surfaces of
every sort in perfect order.
Ashlar and well-laid brickworki
Brickwork, ashlar and stoneware in an inferior con
dition : rubble in cement or plaster, in good order.
Canals and rivers in earth of tolerably uniform cross-
section, inclination and direction, in moderately good order
and regimen, and free from stones and weeds.
Rivers and canals with earthen beds in bad order and
regimen, and having stones and weeds in great quantities.
Experience is required for the assignment of the correct value to n. Its
usual value for the earthen channels of an ordinary canal system in normal
condition would be '025.
The calculation of discharges from hydraulic formulas is much facilitated
by the use of Tables made for that purpose. In India, where discharges
are measured in feet, Higham's "Hydraulic Tables" and Jackson's "Canal
and Culvert Tables " are most in favour. " New Tables for the complete
APPENDIX.
273
solution of Ganguillet and Kutter's Formula for the flow of liquid in Open
Channels, Pipes, Sewers and Conduits," by Colonel E. C. S. Moore, R.E.,
M.S.I., will also be found useful by calculators who work with English
measures. In Egypt, where the metrical system is current, " Elementary
HydrAlios," by Willcocks and Holt, is a safe and simple guide to the
practical use of hydraulic formulas. " The Civil Engineer's Pocket Book,"
by Trautwine, shows how the formulas should be used in both cases, that
is, with English and metric measures. But it is, perhaps, advisable, in
dealing with formulas which, to many, may be sufficiently intricate without
unnecessary complication, to make use of a book of reference on the sub-
ject which deals exclusively either with formulas and coefficient values
adapted to English measures, or with those adapted to metric measures ;
and not to one which, like this Appendix, attempts to deal with both.
However, as this book may, on occasion, possibly be available when others
are not, the two following Tables are given, from which the values of c in
Kutter's formula may be obtained for the usual value of « — viz., •025—
applicable to the ordinary channels of a canal system.
TABLE III.
(For use with English Measures.)
Kutter's, values of c in the Formula V = c V R S for ordinary
CHANNELS IN NORMAL CONDITION, WHEN » = '035.
Hydraulic
Mean
Depth R
s
s
s
S
s
s
s
1
I
I
I
1
I
z
In feet.
40,000
20,000
10,000
5,000
3,500
1,000
100
•10
17
20
32
34
35
27
37
■20
24
26
39
31
33
34
34
•40
33
35
38
40
43
43
44 ,
•60
38
41
'^
46
47
48
49
•80
43
46
48
50
51
53
53
I'OO
47
49
53
54
55
56
56
i'50
55
57
59
60
61
63
63
2-00
61
62
64
64
65
66
66
3-00
70
71
71
71
71
71
71
3-38
72
72
73
72
72
73
73
4'oo
78
77
76
76
76
75
76
6-0O
88
85
84
83
81
81
81
8-00
96
91
88
87
85
84
83
10-00
103
96
92
89
88
^l
86
I2"00
107
99
94
92
90
88
87
i6'oo
"5
106
99
94
93
91
90
20"00
121
no
102
98
96
94
93
30-00
133
118
108
103
99
96
95
50-00
147
137
"i
108
104
10 1
100
75-00
157
133
118
III
106
103
102
100-00
163
137
131
"3
108
105
104
I.
274
APPENDIX.
TABLE IV.
(For use with Metric Measures.)
Kutter's values of c in the Formula V = c a/ R S for ordinarv
CHANNELS IN NORMAL CONDITION, WHEN H = "025.
Hydraulic
s
s
s
s
s
s
s
Mean
Depth R
I
_Z_
in metres.
40,000
20,000
10,000
5,000
3,500
•025
9
10
11
12
13
13
14
•05
12
13
15
16
17
18
18
•10
17
18
19
20
21
22
22
■20
22
23
24
25
26
27
27
•30
26
28
29
30
30
31
31
■50
31
33
33
34
34
35
35
I -00
40
40
40
40
40
40
40
2-00
50
48
47
46
45
45
45
3-00
56
53
51
49
48
48
47
5 '00
64
59
54
53
52
51
50
lo-oo
75
66
60
57
55
54
53
15-00
81
71
63
59
57
56
55
20-00
85
72
64
60
58
57
56
30-00
90
76
67
62
60
58
57
The formulas (2), (4) and (5), for calculating the discharges of sluices,
weirs and syphons, apply to any system of measures, to the metric as well
as to the English. But it is necessary that the head, the length or area,
and the acceleration of gravity ig) should all be in the same unit — either all
in feet, or all in metres, or all in any other unit of measurement. The
discharges will also be in the cube of that unit. The value of g, as has
been stated already, is 32'2 feet in English measure, and 9-83 metres in
metric. The values of c given in the following table are the same what-
ever system of measures may be used ; since c in each of the formulas (2),
(4) and (5) = actual discharge ^ relation which is independent of
"' theoretical discharge
systems of measures.
TABLE V.
Values of c generally employed in practice with discharge
formulas of sluices, weirs and syphons. formulas (2), (4)
and (5).
Description of Discliarge Waterway.
-Ordinary lock sluices and small sluices ...
Clear overfall weirs
Small regulator openings with shallow water
Coefficient c.
•62
•6a
•57
APPENDIX. 875
TABLE v.— continued.
Description of Discharge Waterway.
Coefficient c.
Regulator openings, under 6 feet or z metres in width,
with recesses in the piers
■6z
Ditto, ditto, with straight continuous piers
•72
Regulator openings between 6 and 13 feet (2 and 4 metres)
in width, with recesses in the piers
•73
Ditto, ditto, with straight continuous piers
•82
Regulator openings over 13 feet (4 metres) in width,
with recesses in the piers
•82
Ditto, ditto, with straight continuous piers
•92
Short straight pipes as in syphons
■82
Short bent pipes as in syphons
■72
Formula (3), V ^ c \/ R S, for open channels is of more practical
use in the preparation of a project — to determine, for example, the dimen-
sions of a canal or the possible maximum discharge of an existing natural
waterway — than it is to ascertain the actual discharges of flowing canals.
The more usual way of gauging actual discharges is to ascertain the mean
velocity by direct observations made with floats. The mean velocity
itself may be observed by special floats in the form of rods weighted so as
to maintain a vertical position, and of such lengths that they float with
their lower ends just clear of the bed. The rate of travel of these rods
should be observed along lines in the direction of the flow and equidistant
from one another across the channel. The mean of all the observed
velocities will give tht mean velocity.
But the more ordinary method employed is to observe the maximum
surface velocity, and from it to calculate the mean velocity. All the
apparatus required is a watch, an empty bottle or other simple float, and
means of measuring the cross sections of the channel and intervening
length which will be used as the " run " for timing the rate of travel of the
float. The mean velocity will then be obtained from the observed maxi-
mum surface velocity by the use of the following formula, in which V is the
mean velocity, U is the maximum surface velocity, and c is a coefficient
having the same values as in formula (3), V = c -/ R S, as given in Tables
I. and II. for English and metric measures respectively. These formulas
which follow apply only to ordinary canals, drains and water-courses on
straight reaches of uniform section.
Formula (6 A). V = U X ^-.^ , ^ for English measures (c values of
Table I.).
Formula (6 B). V = U X — x~ for metric measures (c values of
Table II.).
It will be found that, if there are substituted, in the upper and lower
T 2
276
APPENDIX.
equations respectively, values of c from Tables I. and II. for corresponding
values of R — as, for instance, for R = yaS feet. Table I., and R= i metre,
Table II. — the two expressions wUl give the same numerical result. The
Formula (6 C), V = Ci U, can, therefore, be substituted for either, and the
values of c be tabulated. This has been done and the following table is
the result.
TABLE VI.
Values of c, in the Formula V = Cj U for finding mean from
SURFACE MAXIMUM VELOCITY.
Hydraulic
Material of bed and sides of Cliannel.
Hydraulic
Mean Depth R
in feet.
Plastered.
Planed Planks.
Dressed Stone.
Brickwork.
Rubble
Masonry.
Earth.
Mean Depth R
ui metres.
I -00
2'00
3'00
3-28
4'oo
5-00
6-00
6-50
8-00
lO-OO
I3"00
i8-oo
30"00
yo'oo
Inf.
15
■85
•85
•85
■85
•85
•85
•85
■85
•85
is
•85
•85
•85
•83
•83
13
■83
•83
•83
•84
•84
•84
•84
•84
■84
1'^
•84
■84
•77
•79
•80
•80
•81
•81
•81
•81
•82
•8z
•82
•82
•82
•82
•82
•65
•71
•73
•74
•75
•76
■77
•77
•78
•78
•79
•79
•80
•81
■81
•30
•60
•90
fOO
I '20
1-50
r8o
2^00
2'5o
3'oo
3-50
5-50
6^oo
21^00
Inf.
Formulas (6 A) and (6 B), and their substitute Formula (6 C), apply to
all canals on reaches where the maximum surface velocity keeps steadily
to midstream, provided the reach itself is fairly straight and uniform.
Willcocks and Holt in " Elementary Hydraulics," written for the use of
engineer students, give the following simple directions as to the ordinary
method in which a discharge observation should be made.
" Select a fairly straight reach of about 3 kilometres in length, put in a
flag on one bank at about the middle point, taking care that the central
velocity is the maximum. Measure 25 metres upstream and 25 metres
downstream, and put up two more flags, and three flags exactly opposite
these on the other bank. Take three cross sections of the canal at these
three places. Take the mean of the two outer sections, and then take the
mean of this mean and the middle section. This last mean is the actual
cross section of the canal. Now allow some twenty circular discs of wood
of about 10 centimetres diameter and 2 centimetres thickness to pass down
the centre of the canal, and record the number of seconds they each take
to pass the interval between the outer flags. The mean of these twenty
API^LJNUIX. 277
observations divided into 50 metres gives the maximum surface velocity in'
metres per second. Find A (area) and R (hydraulic mean depth) from the
cross section in metres ; we have U ; and c^ can be obtained from Table
VI. by noting carefully the actual condition of the canal. Then V =Ci x U
in metres per second, and Q ^ A X V in cubic metres per second. Of
course discharge by surface velocity observations can only be taken when
there is no wind."
If the discharge of a wide river with an irregular bed has to be measured,
a more elaborate method must be adopted. A cross section of the river
must be made with the aid of a steamer to take soundings and of a theodo-
lite to fix the position of the steamer at the moment of taking the soundings.
Ranging rods, iixed on the bank in prolongation of the line of the cross
section, will enable the steamer to take up its position for sounding on the
right alignment. On account of the uneven section the surface velocities
must be observed at numerous points, and the calculation of the discharge
be made separately for each portion of the cross section to which the
observed velocities belong. The total discharge of the river will then be
the sum of the discharges of the subdivisions which have been separately
calculated.
The formula for open channels, Vi=e V R S, as developed in Kuttei's
formula, can be applied to pipe discharges by giving a suitable value to
». For iron pipes in good order, and from i inch to 4 feet diameter, n may
be taken at from "oio to 'oiz according to the condition of the inner sur-
face of the pipe, the lower figures being used if the pipe is in exceptionally
good condition, and the higher figures when the condition is not so good,
though still good.
There are thus six formulas which are most essential for irrigation
engineers, namely :
Formula (i). Discharge Q = A x V for all cases.
Formula (2), Mean v elocity V = c •/ 2 £■ H for sluice-ways,
Formula (3). Mean velocity V = c ^ R S for open channels and pipes.
Formula (4). Discharge Q = | c A ^' 1 g h ior clear- overfall weirs.
Formula (5). Discharge Q = c X I V 2 g a'l ((k + f d^) for submerged
weirs.
Formula (6 A). Mean velocity V=U X ^ . , ^ for English measures
or Formula (6 B), mean velocity V=U X , ^ for metric measures,
or Formula (6 C), mean velocity V = Cj U, in place of Formulas (6 A)
and (6 B}.
APPENDIX III.
BOOKS OF REFERENCE.
In the following list those worlcs of reference only are included which
deal with irrigation, or one of its main sub-heads, in a general way.
Books, reports, proceedings, and pamphlets, which treat of special
irrigation schemes or constructions, are too numerous for accommodation
in an appendix. Catalogues of such works exist in technical libraries.
Irrigation, General.
"Irrigation." Transactions of the American Society of Civil Engineers-
International Congress. 1904.
A collection of papers on irrigation (i) under British engineers, that is, in
India and Egypt ; (2) in Java ; (3) in the United States ; (4) in France ; and
(5) in the Hawaiian islands, with discussions on the papers.
"Irrigation Engineering," by H. M. Wilson. Publishers: Chapman
& Hall, London, and Wiley & Sons, New York. 1903.
The subject is viewed from an American standpoint. Most of the illustrations
are borrowed from the United States, but some are drawn from India and other
countries. A list of books of reference (chiefly American) is given for each
section of the subject.
" Manual on Irrigation Works,'" by B. O. Reynolds. Printed Govern-
ment Press, Madras. 1906.
This book is written with India as the author's standpoint, and is a text-book
for the use of the students of the Madras Engineering College, compiled by one
of the staff.
" Irrigatioii Manual," by Lieut.-Gen. J. Mullins. Publishers :E. and F. N.
Spon, London and New York. 1890.
This is also written from an Indian standpoint. It contains many plates of
irrigation works existing in 1890.
" Irrigation Canals and other Irrigation Works," by P. J. Flynn.
Published San Francisco, California. 1893.
The subject is treated generally, with illustrations borrowed from America,
India and other countries.
" Hydraulic Works," by Lowis D'A. Jackson. Publishers : Thacker & Co.,
London. 1885.
Statistics are given of the hydraulic works and hydrology of England,
Canada, Egypt and India.
' Irrigation Pocket Book," by R. B. Buckley. Publishers : E. & F. N.
Spon Ltd., London ; Spon and Chamberlain, New York ; Thacker &
Co., India. 191 1.
A comprehensive compilation of facts, figures, and formulse bearing on the everyday
work of an Irrigation Engineer,
APPENDIX. 279
Irrigation in Different Countries.
India.
" The Irrigation Worlts of India," by R. B. Buckley. Publishers : E. and
F. N. Spon, London and New York. 1905.
This is the most complete and recent work which treats of irrigation in India
as a whole. The magnificent irrigation works are descrijjed and freely illus-
trated ; and the lessons taught by experience, gained in irrigation Schemes of
large scale and extending over long periods, are recorded. Almost all matters
connected with practical irrigation are dealt with.
"Irrigated India," by Hon. A. Deakin. Publishers: Thacker & Co.,
London. 1893.
This book contains a description of the irrigation and agriculture of India
and Ceylon as viewed by an Australian.
" Irrigation in India," by H. M. Wilson. Printed Government
Printing Office, Washington. 1892.
The subject is presented as viewed by an American engineer.
" Report of the Indian Irrigation Commission," presided over by
Sir Colin Scott-Moncrieif. Publishers : Eyre & Spottiswoode. 1903.
This report contains a record of the evidence collected by the Commission
concerning the facts about Indian irrigation, and its recommendations as to the
policy that the Indian Government should adopt with reference to future
irrigation schemes.
Egypt.
"Egyptian Irrigation," by Sir W. Willcocks and J.I.Craig. Pub-
lishers: E. & F. N. Spon. London and New York. 1913.
This is the standard work on irrigation in Egypt. It contains an account of
its canal systems, and records the experience of the irrigation staff gained
since 1883 and the opinions formed as a result of that experience.
A merica.
"Irrigation in the United States," by F. H. Newell. Publishers:
Crowell & Co., New York.
This book is intended for the edification of pioneer settlers in a new country,
and therefore is not technical. It treats of constructions and methods more or
less primitive.
" Irrigation in Western America,'' by Hon. A. Deakin. Printed
Government Press, Melbourne. 1885.
The author gives an Australian's view of the subject.
"Irrigation in Southern California," by W. Ham Hall. Published
State Office, Sacramento. 1888.
The irrigable regions and the works and projects of Southern California
are described.
Europe.
" Italian Irrigation," by Captain R. Baird Smith, R,E. Publishers :
Smith, Elder Si Co., London. 1855.
280 APPENDIX.
"Irrigation du Midi de I'Espagne," by Maurice Aytnard Publisher:
Eugene Lacroix, Paris. 1864.
" Irrigation in Souttiern Europe," by Lieut. C. C. Scott-Moncrieff, R.E.
Publishers : E. and F. N. Spon, London. i858.
The three foregoing works give general descriptions of the practice of
irrigation in the southern countries of Europe. They are not, however, intended
to be books of reference for engineers intent upon the more purely technical
studies of their profession.
Rivers and Navigation.
"The Improvement of Rivers," by B. F. Thomas and D. A. Watt.
Publishers : Chapman & Hall, London; Wiley & Sons, New York.
This book treats of dredging, training works, spurs, bank protection, flood
banks, storage reservoirs for navigation, locks, lock gates and valves, fixed
dams (weirs), movable dams and regulating apparatus.
" Rivers and Canals," by L. F. Vernon-Harcourt. Published Clarendon
Press, Oxford. i8g6.
This book deals with the flow, control and improvement of rivers, and the
design, construction and development of canals, both for navigation and irrigation,
and gives statistics of the traffic on inland waterways.
Dams and Reservoirs.
" Design and Construction of Masonry Dams," by Edward Wegmann.
Publishers: Chapman & Hall, London; Wiley & Sons, New York. 1911.
Tliis work gives diagrams and descriptions of the existing high dams studied as
a preliminary to the designing of the Quaker Bridge dam and its substitute, the
New Croton dam.
" Reservoirs for Irrigation," by James D. Schuyler. Publishers :
Chapman & Hall, London ; Wiley & Sons, New York. 1901.
Descriptions are given of the various types of dams, and the book is profusely
illustrated. Information is also given about the natural and projected reservoirs
in the United States of America.
" Masonry Dams from Inception to Completion,'' by C. F. Courtney.
Published 1897.
This small book describes shortly the method of designing and constructing
dams.
" Indian Storage Reservoirs with Earthen Dams," by W. L. Strange.
Publishers : E. and F. N. Spon, London and New York.
This work treats fully of the design and construction of earthen dams, and of
the storage problems connected with them, based on the practice of the engineers
of India in the Bombay Presidency.
Drainage and Reclamation.
"The Drainage of Fens and Low Lands," by W. H. Wheeler.
Publishers : E. and F. N. Spon, London. 1888.
This book gives a general description of works and machines used in draining
low lands.
APPENDIX. 281
Construction.
" Design of Irrigation Works," by William Bligh. Publishers : Archibald
Constable & Co., London.
This book deals with the theory of design and its practical application to
Irrigation Works, with full illustrations ; design of existing works are critically
examined.
" Irrigation Development," by W. Ham Hall. Published State Office,
Sacramento. 1886.
A detailed study of irrigation legislation in France, Italy and Spain is made
with the view of framing irrigation laws adapted to American conditions.
APPENDIX IV-
NOTES. 1919.
Note I to page 7. Results of irrigation reform in Egypt.
The Report of the Ministry of Public Works, Egypt, for 1914-15,
summarises the results of irrigation administration in Egypt in the
following passage : —
" The area cultivated has increased by forty-three per cent, since
1882, and crop has increased by sixty-two per cent. . . . During the
past thirty years an annual average of 30,000 acres of entirely new land
have been added to the taxable soil of the country and now produce
two crops a year ; an average of 40,000 acres a year have been con-
verted from the one-crop system of basin irrigation ; and, whereas the
average area that went without water from the flood each year was
about 90,000 acres, an average of not more than 1,000 acres or so suffer
in that way now."
Note 2 to page i. The Lower Chenab Canal, Punjab.
The following is a quotation from the Government of India's Review
of " Irrigation in India for the Year 1916-17 " : —
" The Lower Chenab Canal is easily the most productive canal in
India. It irrigates 2^ milhon acres, and in the year under review pro-
duced a net revenue of 141 lakhs of rupees on a capital outlay of 324
lakhs, a return of 43J per cent. The accumulated surplus revenues
from this canal, after paying interest charges, amount to no less than
1,271 lakhs of rupees."
Note 3 to page 19. Canal off-takes from rivers.
As regards the siting of the channel which forms the off-take of a
canal from a silt-laden river, it has been suggested that the aUgnment
of such a channel should not make an acute angle with the direction of
the current below the point of off-take, nor even a right angle, but an
obtuse angle ; or, in other words, an acute angle with the direction of
the current above the point of off-take. Sir WilUam Willcocks, in his
projects for the irrigation of Mesopotamia (publishers, E. & F. N.
Spon, 191 1), has deliberately designed canal oS-takes in this way with
the object of avoiding silt trouble. For instance, the Left Euphrates
Canal is shown on his Plan 48 taking off the Euphrates above the
Feluja Barrage in a direction at fnrst opposite to that of the flow of the
APPENDIX. 283
river upstream of the barrage, the head reach of the canal curving round
till the proper general alignment is attained.
Note 4 to page 37. Summer crop area of Egypt.
It appears from the Report of the Ministry of Public Works, Egypt,
for igiij — 1915, that it is now reckoned that in Egypt 50 per cent, of the
gross area of perennially irrigated land is annually put under summer
crop. This is evident from column V. of the statement showing the
areas and water requirements of " the Existing Cultivation and Possible
Further Extension in Egypt."
Note 5 to page 50. Water requirements of Egypt.
The calculation of the additional water required in Egypt, given in
the statement referred to in the foregoing note, is based on an allowance
of 28 cubic metres a day for 150 days per acre of summer crops other
than rice, and of (28 x 3 = ) 84 cubic metres a day for 75 days per acre
of rice. The conclusion reached is that the total additional water
required by Eg5rpt, over and above what the enlarged Assuan reservoir
and the natural discharge of the river supplies, is 9,555 million cubic
raetre^. The same Report gives the content of the Assuan reservoir as
2,400 million cubic metres. The sum of these two figures — 12,000
million cubic metres nearly — should be used when comparing this 1915
estimate with that of ten or twelve years earlier — namely, 6,000 million
cubic metres before the Assuan reservoir contribution was taken into
account. The later estimate of requirements is thus double the earlier
one. The increase is due to —
(i) The assumption that 50 per cent., instead of 40 per cent., of the
gross area is annually under summer crop ;
(2) The substitution of 150 days for 100 days as the period during
which storage water is required ;
(3) The assumption that the present available supply is insufficient
in a low summer to allot any of it to the existing rice area ; and
(4) The adoption of 84 cubic metres a day per acre of crop, instead
of 50, as the proper allowance for rice.
The estimate made with these data gives a result which may safely
be called liberal.
The present additional requirements may be met (i) by storage in
the proposed White Nile reservoir (see the note following), (2) by
arrangements to minimise the loss due to evaporation in the Sudd
region, and (3) by storage in Lake Albert.
The White Nile reservoir is credited with a probable effective storage
of 3,000 million cubic metres in normal years. The official estimate of
requirements is calculated on the basis of a low level year such as 1914.
The estimate of the means of supply should be on the same basis. The
White Nile reservoir must, therefore, be credited with something less
than 3,000 millions, say, 2,000 millions.
The prevention of loss in the Sudd region was assumed on page 56 to
284 APPENDIX.
be equivalent to an effective storage of 1,700 million ciibic metres
(about two-thirds of 2,500 millions). This figure was obtained by
calculating with a base of 100 days only, ignoring the gain during the
rest of the year. But, if the 120 days allowed below for effecting
storage in Lake Albert is excluded, there will remain in the winter and
summer seasons 245 days to take a9count of in reckoning the quantity
gained by the prevention of loss by evaporation. Assuming that the
daily gain is 300 cubic inetres a second (as on page 54) over a period of
245 days, the quantity becomes 6,5oo miUions. Allowing for a loss of
one-third on its journey to Egypt, the net amount becomes 4,400
million cubic metres. Of this the summer contribution would be wanted
for immediate use. The winter addition could be stored to the extent
of 1,000 million in the White Nile reservoir, and the remainder be kept
back in Lake Albert till it was wanted.
Thus, in a bad year, the White Nile reservoir and the Sudd region
economy would together supply (2,000 + 4,400 =) 6,400 million cubic
metres, or about 3,000 millions less than the full estimate of 9,555
millions.
Lake Albert is relied upon by the P. W. Ministry to make good the
balance — " to ensure sufficient water to meet the ultimate requirements
of Egypt under the fullest cultivation." The possibihties of storage in
Lake Albert were discussed in The Engineer of September 23rd, 1904.
It has no doubt enormous capacity as a storage reservoir, but the
effective storage possibihties are limited to what evaporation spares of
the run-off of the rainfall. Sir William Garstin, in his " Report on the
Basin of the Upper Nile " (1904), states that " the mean discharge of
the Bahr-el-Gebel, at Wadelai, as worked out by Mr. Craig, is 769 metres
cube per second. This equals a total of some 24,250,000,000 metres
cube per annum." Now, the winter and summer discharges of the
Blue Nile are allotted to the Sudan. Moreover, a minimum discharge
from Lake Albert of 25 million cubic metres a day, or 287 cubic metres
a second, is required to provide for navigation. If the remainder —
482 cubic metres a second — ^is retained in the lake during the 120 days
of flood, the amount stored would be 5,000 million cubic metres, and
this could be reserved for use in Egypt during the 245 days of winter
and summer. Allowing for 30 per cent, of loss on the way, the amount
that would reach Egypt would be 3,500 million cubic metres.
So, if the official estimate of 9,555 million cubic metres is a correct
one, it appears that the storage possibilities of the equatorial lakes are
not much more than sufficient to meet the balance of the ultimate
requirements of Egypt — the conclusion arrived at on page 57.
Note 6 to page 52. The White Nile Reservoir.
A project for storage of water on the White Nile has been approved.
The general lines of the project were described on pages 702 and 704 of
the third edition (1913) of " Egyptian Irrigation." by Willcocks and
Craig. A barrage is to be built on the White Nile at Gebel Auli, about
APPENDIX. 285
twenty miles upstream of Khartoum, to form a reservoir of a net
capacity of about 3,000 million cubic metres. (The complete scheme
also contemplated another barrage at Gebelein, still higher up the river,
which, apparently, is not included in the project as at present approved.)
This storage scheme takes advantage of the peculiar conditions which
exist in the tail reaches of the White Nile during the flood season.
When the Blue Nile is in flood and rising, it fills the whole trough of the
Nile below Khartoum and holds up the White Nile water, and all, or
most of, the water of the White Nile is stored in the natural reservoir
formed by the valley through which it flows. In proportion as the
Blue Nile flood subsides the water stored in the White Nile valley adds
itself to the river discharge flowing forward to Egypt. In consequence,
the subsidence of the flood in Egypt is retarded sometimes to an extent
which is injurious, or eveii dangerous. The projected barrage at Gebel
Auli will remain open during the rising flood while the Blue Nile is hold-
ing up the White Nile ; but, as soon as the rise ceases and the White
Nile water begins to move forward, the barrage will be closed against it
and the accumulated water be retained for use later on. By this scheme
two advantages are secured : the period of danger to Egypt in -a high
-^flood is shortened by the fall of the river being accelerated ; and a
valuable quantity of water is kept in hand until the time of need.
Note 7 to page 61. The Triple Canal System of the Punjab.
In the Government of India's Review of Irrigation for 191 6-1 7
the completion of the Triple Canal Project, so far as the main canals
are concerned, was announced.
" The Triple Canal Project was commenced in 1905 ; of its three
component parts the Upper Chenab Canal was opened in 1912, the
Lower Bari Doab in 1913, and the Upper Jhelum in 1915. . . . The
Upper Chenab Canal, with a bed width of 240 feet, a full supply depth of
12 feet, and a capacity of 11,700 cubic feet per second is, it is believed,
the largest irrigating channel in the world."
The cost of execution of the project is. In round numbers, ;^7,ooo,ooo.
If the annual irrigation reaches 2,000,000 acres, which it is not unlikely
to do, the net revenue will be nearly ;^56o,ooo, and the return on the
capital cost will become 8 per cent.
Note 8 to page 176. Canal Sections.
There are other considerations, besides the_ prevention of scour and
deposit of silt, to be borne in mind when canals are being designed. The
'following passage occurs in a paragraph dealing with " Seepage Losses
in Canals " in the Report of the Ministry of Public Works, Egypt, for
1914— 1915 :—
" The experiments indicate that although wide shallow canals may
silt less, yet the loss by seepage in them is greater than in narrow and
deep canals, the seepage being directly proportional to the width and
wetted perimeter, but proportional only to the square root of the
hydraulic mean depth. This factor should influence canal design in
286 APPENDIX.
Lower Egjrpt where eventually large areas will be drained by lift, so
that seepage losses should be jealously guarded against."
Note 9 to page 245. River protective and training works.
Sir John Ottley, K.C.I.E., formerly Inspector-General of Irrigation
in India, in a review of the first edition of this book in the R.E. Pro-
fessional Papers of July, 1907, considers the distinction made between
protective and training works as " somewhat fanciful," and is not a
beUever in powers of persuasion. He writes : " It is quite certain that
those of&cers in Northern India who have the largest experience in
river work are of one mind in agreeing with Mr. Good that a river should
be ' fought and not merely tickled.' For ten or twelve years prior to
1887 ' persuasion ' was tried at Narora and miserably failed ; since
1887 the Ganges has been ' fought ' with conspicuous success and at no
greater an expenditure of money than before."
Note 10 to page 252. The cotton crop of Egypt.
The passage to which this is a note was written in 1907 as it stands
now. The Report of the Ministry of Public Works, Egypt, for 191 1
(published 1913), contains this paragraph from the pen of the Under
Secretary of State : —
" It is extremely likely that in the case of 1909 it was not the removal
of the Sharaqi Decree itself at a.n early date, but the superabundance of
water at the disposal of the cultivators and the high levels in the canals,
which they so freely took advantage of, which did the damage to that
year's cotton crop. In future years it is the intention of the Depart-
ment to pass down main canals at this period of the year just sufftcient
to meet requirements. Any excess over this quantity will be passed
into the river channels and allowed to flow to the sea."
This points the moral drawn on page 252.
The cotton crop of 1909 — a year of high summer river discharges
exclusive of the reservoir addition — yielded 5,000,772 kantars, being at
the rate of 3-24 kantars per acre of crop ; whereas the crop of 1900 — the
year of the lowest Summer supply in the river on record and without a
reservoir to help — ^yielded 5,427,339 kantars, being at the rate of
4.42 per acre of crop.
In the Report of the P. W., Egypt, for 1912 (published 1914) a
table is given showing the areas planted with cotton and the yield for
each year from 1891 to 1912. From the figures therein given it appears
that, since the Assuan reservoir first came into action in 1903, the area
of cotton crop has increased by one-third, whereas the total 5rield has
increased by one-sixth only ; and the jdeld per acre has decreased from
an average of 5 kantars an acre to 4-3. Since 1912 the cotton crop
returns show no improvement. The 1915 and 1916 crops pelded results
inferior to those of the 1900 crop as regards both the total yield and the
yield per acre of crop.
INDEX.
Absorption by soils, 31, 65 ; in basins,
21, 22 ; in canals, 35, 216 ; in reser-
voirs, 41, 70, 71 ; in the Nile marshes,
52 — 55 ; in transit from reservoir, 48,
64
Abu Bagara Canal, Egypt, 18
Abyssinia, region of rainfall, 2
Acre- foot, 33, 34
Adrainistiation of canals, America, 232,
233 ; France, 232 ; Spain, 231
Afflux above river weirs, 112
African lakes, 46
Afiica, South, storage, 59, 63 ; de-
velopment, 59, 63
Agriculture and irrigation, 30, 250, 251,
252
Albert Edward Kyanza, 46
Albert Nyanza, 46, 54, 55, 56, 57
Alexandria, Mex pumping station, 256
Algeria, Khamls undersluice, 93 ; silt-
ing up of reservoirs, 92
Alicante dam, 92, 102 ; water rates, 228
Alignment of channels, 171, 172; dams,
91; drains, 173; river weir, 114;
" Sudd " channel, 55
Almanza dam, 82, 102 ; water rates, 228
America, canal administration, 232, 233 ;
capacity of reservoir, 33 ; Chamoine
system in, 108 ; " duty " of water, 32 ;
inland waterways, 259 ; irrigation,
108 ; new Croton dam, 103 ; river
banks, 240 ; water rates, 227 ; Western
States, development, 63 ; windmills,
106
American dams, 71, 79; type of river
regulator, 108
Andalucia, Spain, 172
Anicut, Coleroon, 135 ; Grand, 29, 1 1 1 ;
Indian type of weir, 107 ; site of, 113:
sluices, 112, 113; Sone, 113
Anicuts, silt deposit above, 112, 113,
114
Apparatus, lifting, 43
Apron, protective, Assuan dam, 100
Aprons of clay, 130, 132; escapes, 197 ;
impermeable, 130
Aqueduct, Nadrai, 67, 68
Aqueducts of iron, 207 ; of wood, 207 ;
over drain^es, 203 — 206
Area, catchment, 31 ; cultivable, Egypt,
7 ; irrigable, 212 ; irrigated by Divi
pumps, 139, 257 ; irrigated, India, 8 ;
Komombos scheme, 139 ; of arid re-
gions, U.S.A., 9 ; of crop, limitation
of, 213, 218, 222, 223 ; of crop, rate
on, 213, 215; of crop sown, 41; of
Dongola province, 105 ; of drainage
served per pump, 257 ; of Egypt, 50 ;
of Lake Albert, 56 ; of Lake Moeris,
47 ; of St. Lawrence lakes, 45, 46 ; of
tanks, India, 61, 62 ; under well irriga
tion, 43, 44
Areas commanded, 178 ; gross, 178 ;
inundated, Egypt and India, 25, 26 ;
irrigated by pumps, 138, 139 ; irrigated
by tanks, 62 ; irrigated, India, 62 ; of
cultivation, 33 ; of lakes, 46 ; un
flooded, 18
Arid conditions, 2 ; regions of Canada,
9 ; regions of Mexico, 9 ; regions of
U.S.A., 9, 58
Arid regions, U.S.A., require storage,
58 ; west of U.S.A., windmills, 105,
106
288
INDEX.
Arizona, ancient irrigation works, 30 ;
miner's inch, 34
Armant pumping station, 138
Artesian wells, 44
Ashlar covering for floors, n6, 141, 142 ;
covering of Delta barrage floor, 130;
floor below falls, 195
Assessment, land tax, 226, 227
Assessment of water rales, 213
Assiout barrage design, 127, 131 — 133,
149 ; floor, 142 ; foundations, 145,
149, 150; piles, 151, t55
Assiout, head sluice above barrage, 192
Association of cultivators, 232
Assuan dam and reservoir, 50, Jt > de-
scribed, 96 — 100 ; efiect of, incom-
plete, 7 ; Egypt's requirements before
making, 56 ; locks, 262, 263, 265, 266 ;
maximum pressure, 102 ; of necessity
of masonry, 80 ; raising of, 52, 99,
100; results of building, 28
Assuan reservoir and cotton crop, 251,
252 ; and dam, 51, 52 ; capacity, 56,
70 ; described, 97, 98, 99
Atcherley's theory of dam stresses, 81,
100
Atfeh pumping station, 135—138
Australia, Mundaring dam, 88, 102, 103
Ayat pumping station, 138
B.
Babylon and irrigation, 4, 5, 29
Babylonia and irrigation, 3, 4, 7, 28
Backing up of water, or afflux, 1 1 2
Baikal lake and Yenisei river, 46
Baird-Smith, Capt. R., on Italian" duty,''
38
Baitumee weir, 114
Bakw, Sir B., on dam designs, 81, 82
Baltic and river navigation, 47
Banks. See also Embankments
Banks, basin, cuts in, 15 ; cross, of
basins, 21 ; dimensions of, 24, 25 ;
enclosing foundation area, 143, 145 ;
longitudinal, 15 ; protection of slopes
of, 24 ; protective, 14, 237 — 243 ; pro-
tective, action of, 13
Bari Doab canal, "duty" on, 41 ; loss
of water, 35
Barrage, Assiout, 127, 131— 133, 142;
Delta, III, 116, 128—130, 13s, 137;
Delta, restoration, 127, 130, 136 ;
Egyptian type of weir, 107 ; Zifta,
131 — 134, 142 ; Zifta, floor, 142
Barrages of Egypt, 112, 134
Base of " duty " of water, 40, 41
Bascule girders, 262, 263
Basin banks, cuts in, 15 ; dimensions,
24, 25 ; protection of slopes, 24
Basin crops, 24, 28
Basin escape design and discharge, 22, 23
Basin escapes, 15 — 17, 21 — 24, 194, 197
Basin feeder, head and off-take, 19—24 ;
silting of head of, 21 ; syphon under,
21, 22 ; work of, 16, 17, 18
Basin filling, 23, 24
Basin inundation, depth of, 20, 22
Basin land conversion, 28 ; value of, 28
Basin regulator design, 23, 192, 193
Basin regulators, 15, 16, 17, 21
Basin system, 3, 15, 16, 17, 29
Basin system, Egypt, 26 ; high level
canal, 16, 18 ; principles of working,
16, 23 ; project for, 19 ; sluices, 21 ;
supply, 16, 17; syphon canal, 16, 18
Basins, contents of, 21 ; deposit of silt,
16; emptying, 23, 24; feeder-sluices,
17 ; period of emptying, 19, 20, 22 ;
period of filling, 19, 20, 22 ; size of,
20 ; sluices, 21
Batter of lock walls, 265
Bear Valley dam, 92, 93
Belgium, inland waterways, 25>>
Bench flumes, 207
Bengal crops, 37
Beresford's filter, 124, 125
Betwa dam, 82, 84
Bhatgarh dam, 95, 96, 100, 102
Bhatgarh reservoir, 97
Blue Nile in Abyssinia, 2
Bombay, consolidated rate, 227 ; Deccan
districts, 38 ; Maladevi tank dam, 73 ;
Orissa and Midnapore canal systems,
258 ; waste weirs of reservoirs, 69
Books of reference, 278 — 281
Bor, the Nile at, 5 5
Boul6 shutters, 107, 108
Brahmini weir, 114
Branch canal discharges, l8j | head
sluices, 192
INDEX.
289
Branch canals, 171, 180, 184
Branch drains, 187, ]88, 189
Bleach in banks, 241, 242
Buckley, Mr. R. B., or. canal discharges,
177. 1/8; on the Chenab canal, J;
on the Coleroon anicut, 134, jj5 ; on
the Delta barrage weir, 124 ; on
" duty " of water, 41, 42 ; on " duty "
for Spain, 39 ; on flow-oft, 65 ; on
navigable waterways, India, 258 : on
Narora weir failure, 118, ; 19 ; on rota-
tions, 217 ; on the Trebeni canal head
sluice, 190, 191
Budki superpassage, 205
Burmah, consolidated rate, 227 ; Thap-
angaing aqueduct, 206
Barra weir, 1 14
Bywash of reservoir, 67
Bywashes in basins, 1 5
C.
Cache-la-Foudre valley, Colorado, 60
California, curved dams, 92 ; " duty " of
water, 39 ; miner's inch, 34 ; San
Di^o flume, 207 ; Southern, dams,
79 ; Turlock and Modesto districts, 9;
Turlock dam, 84 ; wells, 44
Camera curtain, 107, 108, 202
Canada, arid regions of, 9 ; Western,
development, 63
Canal, Abu Bagara, Egypt, l8 ; adminis-
tration, America, 232, 233 ; adminis-
tration, France, 232 ; and well water
compared, 44, 45 ; Bari Doab, loss of
water on, 35 ; Bari Doab, "duty " of
water on, 41 ; branch, alignment, 171 ;
Chenab, effect of making, 7 ; Chenab,
exceptional case, 8 ; cross-sections,
178, 179; dimensions, 178, 179; dis-
charges, 177, 178; escapes, 192 — 194,
197 ; falls, 177, 192, 19s — 197, 260
Canal, flood, design of, 20, 21 ; Ganges,
loss of water on, 35 ; gradient, 1 73,
177; head, "duty" at, 41; head
sluice, 174, 190 — 192 ; high level,
basin system, 16, 18; irrigation area,
India, 6.2 ; loss of water in, 35, 36 ;
Mahmudia, 137 ; Main, alignment,
171; of Babylon, 29; of Hammurabi,
I.
4, 29 ; project and evolution of scheme,
30 ; spurs, 244, 245 ; syphon, basin
system, i6, t8 ; system described,
171 ; system, design, 48 ; weirs, set
canal falls ; works, neglect of, 4 ;
velocity, 173 — 177
Canals, alignment of, 171, 172; basin,
Egypt, 26 ; flood, 25, 26 ; inundation,
relieving pumping stations, 138; Meso-
potamia, 4 ; of inundation in basin
systems, 14, 15 ; of inundation, India,
25, 26
Capacity, Assuan reservoir, 97, 98, 99 ;
Bhatgarh reservoir, 97 ; Marikanave
reservoir, 89, 90, 91 ; of Albeit Nyanza,
56; of drains, 187, 188, 189; of
reservoirs, how determined, 70 ; o(
reservoirs, how expressed, 33
Cape Colony, South Africa, 26, 27
Cascades on canals or escape channels,
194, 196
Caspian and river navigation, 47
Castellon, land values, 1 1
Cast-iron piles, 151, 152, 155
Castlewood reservoir dam, 79, 80
Catalonia, water rates, 228
Catchment and flow-oS, 59, 66 — 68 ;
and rainfall, 43, 67, 68 ; areas, 2, 31,
58 ; discharge formulas, 69; diversion
of supply of one to another, 59, 60, 61 ;
of reservoir, 63, 64, 65 ; Periyar, 60 ;
position and nature of, 45
Cauvery river weir, 29
Cement grout used for closure of springs,
150; used for pipe syphon ends, 168,
169
Cement grouting, advantages of, 163 ;
apparatus 152, 156, 158, 159; at the
Delta barrage, 157, 158, 159; for
foundations, 157 — 163, 166, 167 ;
joints, Detroit tunnel, 170 ; of the
Delta barrage foundations, 163, 164,
165 ; Shubra, 156, 157, 166, 167
Cement, proportion in grouied masonry,
161
Central Provinces, India, rainfall, 2
Chain of basins, 15, 16, 18
Chaldea and irrigation, 3, 4, 5
Chamber of locks, 261 ; walls of locks,
264, 265
U
290
INDEX.
Chamoine system of closure, io8
Channel through Nile swamps, 55, 56, 57
Channels, classification of, 171
Channels, underground, 43
Charles III. of Spain, dams built in reign
of, II
Chenab Canal, effect of, 7 ; exceptional
case, 8 ; notch falls, 198, 199 ; river,
25, 61 : weir, 114, 116, 121, 122
Classification of dams, 71 ■
Clay apron, 130, 132
Closure by horizontals, 200, 201 ; by
iron gates, 201,202; by roller curtains,
202 ; by vertical needles, 200 ; of Delta
barrage gates, 137
Coleroon anient, 135
Collins, Mr. M. R., on land values,
Transvaal, 9
Colorado, ancient irrigation works, 30 ;
diversion of flow-off, 59, 60 ; Castle-
wood reservoir dam, 79, 80; "duty"
of water, 39 ; High Line canal,
207
Commanded areas, 178
Commander Felix Jones on Mesop itamia,
S
Commission, Indian irrigation, 58
Como, Lake, 46
Compressed air for foundations, 153
Concessions for irrigation, Spain, 232
Concrete bed of pipe syphons, 211
Concrete casing of pipe syphons, 211
Conflict of irrigation and navigation, 259
Congo, lake source of river, 46
Consolidated land and water rate, 227
Consorzio of Piedmont, 231
Constance, Lake, 46
Construction works, 141
Control of irrigation by Government, 22S,
232
Core of steel plate, 79
Core wall of weir, foundations of, 154
Core walls in dams, 7 1 , 75 — 79
Cost of Delta barrage restoration, 136 ;
of Divi pumping station, 257 ; of land-
owners' operations, 250, 251 ; of
lifting water, 139, 140; of lifting
water, Divi island. 257; of pumping,
136, 256, 257; of pumps, 136; of
working Delta bnrrage, 136
Cotton crop, 251, 252
Cotton crop, Egypt, 7
Cotton, water allowance, a 18, 22a ;
watering intervals, 218, 231
Cotton, Sir A., and navigation, 258
Country slope, 173, 177
Crib weir, 109
Crop area, sown, 41 ; gross, Egypt, 37 ;
rate on, 213, 215
Crop areas irrigated by machines, loj,
106
Crop, cotton, Egypt, 7; flood, Egypt,
38 ; maize, Egypt, 7 ; rice, Egypt, 37 ;
rice, India, 38; value of cotton, 136
Crops, basin, 24, 28 ; Bengal, 37 ; cost of
raising, Egypt, 7 ; double, remark by
Megasthenes, 7; Egypt, 37; Egypt,
after flood, 3 ; Egypt, entirely depen-
dent on irrigation, 8 ; flood season, 25 ;
hay, France, 10 ; insurance of, 31 ;
kharif and rabi, 25, 26, 37 ; perennially
irrigated, 28 ; Punjab, 37 ; requiting
summer waterings, 63 ; saved by irriga-
tion, value of, 8 ; summer, 28 ; under
irrigation, 31 ; United Provinces,
India, 37 ; value of, 28 ; value of,
India, 8; waterings, 34, 36, 37;
winter, 28
Crest shutters, 100, 112, 113, 123, 12$
Cross banks, 21
Cross embankments, regulators of, 23
Cross section of canals, 178, 179
Croton dam, 90, 91, 100
Cultivable area, Egypt, 7
Cultivators and irrigation, 251
Culverts in river banks, 242
Curtains of sheet piling, 151
Curtain walls, 11$, 121, 153, 154
Curtain wells, 120, 121, 122
"Cusec," abbreviation, 32
Cushion below drop wall,lii9
Cuts in basin banks, 15
D.
Dabaya, pumping station, 138
Dam, Alicante, 82, 92, 102; Almanza,
82, 102; Assuan, 7, 28, 50, 51, 32,
56, 96 — 100, 102 ; Bear Valley, 92, 93;
Betwa, 82, 84; Bhatgarh, 95, 96, 100,
102 ; Castlewood reservoir, 79, 80 ;
INDEX.
291
Croton, 90, 91, 100 ; Foy Sagar tank,
77, 80 ; Furens, 82, 87, 88, 91 ; Genii
river, 109 ; Gros Bois, 102 ; Kair
tank, 77, 78 ; La Grange, 83,
84 ; Maladevi tank, 73, 75 ; Marika-
nave, 89, 90, 102, 103; Mundaring,
88, 102, 103; New Croton, 76, 102,
103 ; Nira, 86, 88 ; Periyar, 60, 88,
89; Quaker Bridge, 91, 102; Sweet-
water, 92 ; Titicus, 91 ; Turlock, 84,
85 ; Upper Otay, 92 ; Val de Iniierno,
92, 98 ; Verdon, 102 ; Vyrnwy, 84, 85,
86 ; Walnut Grove, 79 ; Zola, 92,
93
Damietta branch, 137, 138, 238 ; branch
weir, 131 ; flood level, 239
Dams, alignment of, 91 ; American, 79 ;
core walls, 77 ; earthen. South Africa,
26 ; flanks of, 76 ; foundations of, 71,
73t 7S ■' Government work, 236 ;
height of, S9 i insubmergible, 71, go,
83, 100 ; limits to height, 70 ; loose-
rock, 7I> 79, 80 ; of different types, 71 ;
of earth, 71 — 74, 78; of masonry, 71,
72, 78, 80 ; of reservoirs, 57, 58, 59 ;
of South California, 79; of Spain, 11,
82 ; on rivers, 106, 107 ; pierced, 71,
80; Poir^e, 107; pressures in, 102;
rockfiU, 71, 79i 80; "saai," 27;
scouring sluices of, 92 — 96 ; solid, 71,
80; stability of, 81; stresses in, 81;
submergible, 71, 80, 83, 100 ; tem-
poiary, Nile, 137 ; theory of construc-
tion, 81 ; waste-weirs and outlets, 76 ;
water cushion, 83, 84, 85 ; with and
without cores, 71 ; with curved plan,
91, 92
Darro river, Granada, 109
Deacon, Dr., on Vyrnwy dam, 86
Deccan districts of Bombay, storage, 58
Deha barrage, Egypt, III, 116, 128—
«30. '35. '37, '45 : cement grouting
at, 157. '58, 159; grouting founda-
tions ot, 163, 164, 165 ; restoration,
'27, 130, 136, 145—147; water levels,
132; weirs, 114, 122 — 135
Delta of Egypt, and Lake Moeris, 29,
48 ; and water distribution, 128, 131 ;
drainage, 136 ; flood levels, 238 ;
formation of, 13 ; irrigation of, 135,
136, 138 ; training river at apex of,
247
Deltaic branches of Nile, 29, 48 ; river
regulator of, 110
Deltaic formation, 13 ; river banks, 237
Deltas of rivers, growth by deposit, 12;
low seaward margins, 253 ; of India,
formation, 13
Demak, Java, rotations, 223
Demand, accommodation of supply to,
64 ; and supply, 67 ; for water, 31, 32.
49
De Meyier, Mr. J. E., on rotation, Java,
223, 224, 225
Deposit. See also Silt
Deposit of silt, 24, 25, 173—177, 217:
in basins, 16; in reservoirs, 98, 92,
95 1 96 ; locks, 264
Deposit, silt, staunching action of, 35
Deposition of silt, 12, 13, 248
Deposits in canals, 244, 245
Design of canal system, 48 ; of canal
works, 192
Detroit river tunnel, 169, 170
Dickens' formula, 69
Diesel oil engines, 139
Dimensions of canals, 178, 179 ; ol
diains, 186—189
Discharge determined by crop and
" duty," 212 ; formulas for catch-
ments, 69 ; from tanks and reservoirs,
69, 70 ; measurements, 275, 276, 277 ;
Nile, 50 ; of basin escapes, 22, 23 ;
of basin feeder, 21 ; of branch canals,
185 ; of Divi pumping station, 257 ;
of drainages, 206 ; of Kosheshah
escape, 194 ; of lock sluices, 262, 263 ;
of main canals, 185
Discharge of reservoir escape, 67 ; of St.
Lawrence lakes, 46 ; Periyar river,
61 ; required, 36, 37, 38 ; required by
Egypt, so, SI
Discharges, flood, 68 ; flood, Egypt, 38 ;
lake, 32 ; of canals, 177, 178; of dis-
tributaries, 180, 181, 184, 1 8s ; of
drains, 187, 188, 189 ; record of, 68 ;
required, 40; river, 31; summer,
Egypt, 38; through the "Sudd,^
53, 54
Discharging capacity of river, 238
U 2
292
INDEX.
Distiilmtaries of a canal system, i8o—
1 85 ; alignment of, 171 ; rotation by,
217
Distributary cross - section, 182 ; dis-
charges', 180, 1 81, 184, 185 ; loss of
water in, 35
Distribution according to area, 213, 215 ;
affects "duty," 212 ; by rotation, 180,
181, 183, 184; means of, 171— 189;
methods of, 180, 212—226 ; of flood-
water, 16, 17 ; skill in, affects loss, 35 ;
with convenient surface levels, 38
Distribution works, 190 — 211
Diversion from one catchment to another,
59, 60, 61
Divi pumping project, 140, 2S7
Uongola irrigated by sakias, 104
Drainage and irrigation, 172, 182, 183,
185, 186 ; by free-flow, 255 ; by
pumps, 257 ; crossings, 203—208 ;
diverted, 203 ; East of United States,
46 ; inlets, 203 ; in super-passages,
203—205, 209 ; of Delta of Egypt,
186 ; of earthen dams, 74 ; passed by
level crossing, 203, 204, 206, 207 ;
pumping for, 256, 257 ; subsoil, 253,
254, 2SS f syphons, 203, 204, 208 —
211 ; under aqueducts, 203 — 206
Drains, alignment, 173 ; of a canal
system, 18s — 1189 ; overworked, 252 ;
reclamation by, 253, 255 ; relief of,
under rotation system, 183 ; scheme
of, 31
Dredging drains, 189
Drought, years of, India, 8
Duties of Government engineers, 228,
229
' ' Duty '' of water, America, 32 ; as
affected by rain, 42 ; at head of canal,
41 ; at reservoir, 41 ; base of, 40, 41 ;
basis of project, 34 ; calculation of,
34 ; California, 39 ; Colorado, 39 ;
definition of, 32 ; depends on manner
of distribution, 212 ; determination of,
250 ; during rotations, 42 ; Egypt,
33. 34. 37—39. 42. 220, 252 ; equiva-
lent expressions, 268 ; for kharif,
India, 39 ; for rabi, India, 41 ; from
life period of crop, 42 ; high or low,
34 ; India 32, 33, 36—38 ; in irriga-
tion, 32—43 ; in terms of area, 32—
34, 36 ; in terms of discharge, 32 — 34,
36 ; in terms of volume, 32 — 34
Italy, 38 ; Montana, 39 ; of period o?
pressuie, 41, 42 ; of reservoir, 33, 40 :
of whole season, 42 ; on Ban Doab
canal, 41 ; rice, 38 ; shown in annual
reports, 41 ; South of Europe, 33 ;
South of France, 39; Spain, 39;
unit of measure, 32 ; Utah, 39
Dwarf walls below escapes, 197
E.
Eartkbn dams, 71—74, 78
Economy of water, 216, 261, 262
Egypt, Abu Bagara Canal, 18 ; ancient
irrigation, 7 ; and Mesopotamia, floods
compared, 3 ; area, 50 ; as affected by
lakes, 46 ; as illustrating pirinciples,
181 ; Assuan dam, 96 — 100, 102 ;
Assuan reservoir capacity, 70 ; Atfeh
pumps, 137, 138 ; barrages, 134 ;
basin banks, 24, 25 ; basin canals, 26j
basin system, 3, 26 ; canal discharges,
184, 185 ; capacity of reservoir, 33 ;
capital expenditure, 7 ; corn, 3 ; cost
of raising crops, 7 ; cotton crop. 7,
251, 252 ; crops after flood, 3 ; crops
entirely dependent on irrigation, 8 ;
crops, summer, 37 ; cultivable area, 7 ;
decay of irrigation works of, 6 ; delta
of, 29, 48; Delta barrage,* III, 116 ;
Delta barrage weir, 123, 124, 125 ;
development, 63 ; discharges, 38 ; dis-
charge required, 50, 51 ; distributaries,
181, 184, 185 ; drains and drainage,
136, 186, 188, 189; "duty "of water,
33> 34, 37—39. 42, 252 ; flood crop,
38 ; flood discharge of canals, 178 ;
flood levels in delta of, 238 ;
flood season, 3, 38 ; forced labour
abolished, 7 ; formation of delta, 13 ;
forms of spurs, 243, 244 ; gates of
barrages, 1 27 ; Government controls
irrrigation, 228, 234 ; granary of
Rome, 3 ; gross, commanded and
crop areas, 37, 178 ; horizontal closing
plank, 201 ; inundation canals, 26 ;
inundation in, 25 ; irrigated by flood,
12 ; irrigation by inundation, 3 p Irri
INDEX.
293
gation Department, 229, 230 ; irri-
gation of delta of, 135, 136 ; irrigation
record of, 7 ; Kosheshah escape, 194,
195 ; Lake Mareotis, 256 ; Lake
Tsana as reservoir for, 2 ; land tax,
226; Lower, irrigation, 129, 130;
main canal cross-section, 179 ; maize
crop, 7 ; navigable canals, 259 ; needle
closure, 200 ; Nile, its rain-water
carrier, 43; perennial irrigation, 29;
period for calculating duty, 42 ; period
of basin filling, 19, 20, 22 ; pipe
syphons, 167 ; pumps, lo6, 139 ;
rainfall, 2, 3 ; recent history, 49 ;
reclamation of river bed, 248 ; re-
cuperation of, 6 ; reservoir of, 49, 50 ;
rice crop, 37 ; river banks, 337, 240,
341 ; rotations, 184, 216, 218 — 222;
size of regulator vents, 191 ; spurs,
24S, 247 ; storage requirements, 55, 56 ;
summer season, 104; the sakia of,
104 ; the skadouf of, 104 ; training
works, 47 ; under the Pharaohs, 3, 29I;
unreclaimed lands, 253 ; Upper, basin
programme, 23, 24 ; value of land, 7 ;
water allowance, 37, 38 ; watering
periods, 37, 38 ; water rates, 226 ; water
supply, 52, 56 ; waterways public, 235 ;
waterwbeels, 106 ; well irrigation, 43 ;
yield of high and low lands, 255
Egyptian barrages, 112 ; type of river
regulator, 107, 131, 132, 134; weir,
114, 123, 124, I2S
Egyptians, control of inundation by, 3
Elche, Moors first engineers of, 10
Embankments. See also Banks
Embankments, cross, 14, 15 ; cross,
regulators of, 23 ; flood, 237 — 243
Encroachment by river, 243
Engineer, well-irrigation not his pro-
vince, 44
Engineering, irrigation, scope for, 9
England, rainfall, I
Equatorial lakes, Africa, 46, 52, 54, 56,
57
Erosion, by waves, 241 ; in canals, 244,
245 J of bed of watercourse, 12; of
toe of Assuan dam, 99 ; river, 21
Escape, basin, design and discharge of,
2Z) 23 ; by level crossing, 22 ; canal.
design of, 192, 193, 194 ; of basin
chain, 22, 24 ; of reservoir, 65, 67, 69 ;
waterway of reservoir, 65, 67, 69
Escapes, basin, working of, 23, 24 ; of
basins, 15, 16, 17, 21, 22, 24; on a
canal system, 193, 104
Esla canal, water rates, 228
Euphrates and floods, 3, 4, S, 12
Europe, and Philse, J I ; irrigating coun-
tries in, 10 ; natural reservoirs, 46 ;
Southern, "duty" of water, 33
Evaporation afiected by temperature, Jt ;
in basins, 21, 22 ; in canals, 35, 216;
in reservoirs, 41, 50, 59, 70, 71 ; in
the Nile marshes, 47, 52 — 55; in
transit from reseivoir, 48, 64; on
catchments, 65
Expenditure, annual, Divi pumps, 257 ;
by landowner, 250, 251 ; capital,
Egypt, 7 ; capital, India, 8 ; profit on,
India, 8
F.
FAiLtJRB of Chenab weir, 121, 122 ; oi
Delta barrage, 128, 129 ; of Narora
weir, 118, 119
Falls on canals, 177, 192, 195, 196,
260
Farmers and irrigation, 251
Fayum and Lake Moeris, 29, 47 ; and
Wadi Kayan, S* ; waterwheels, 106 ;
weir called nasiah, 199, 200
Feeder canal of basins, 19, 20, 21
Feeder sluices of basins, 17
Felix Jones, Commander, on Mesopo
tamia, 5
Ferro-concrete, 141
Filling and emptying locks, 263
Filter bed, Beresford's, 124, 125, 132
Financial prospects of iirigation scheme,
250, 256
Flood. See also Inundation
Flood canals, design of, 20, 21 ; gradients,
25 ; in India, not inundation, 26
Flood, crops after, Egypt, 3 ; discharge
of canals, Egypt, 178 ; discharges
from flow-off of catchment, 68 ; dis-
tribution, 16, 17 ; earliest recorded,
on Euphrates, 5 ; embankments, 237 —
243 ; extreme low, 21 ; gradient, 68 ;
294
INDEX.
inundation by, Ij, I4 ; irrigation, 26 ;
level, mean, 20, 21 ; levels, rise of,
238 i levels in delta of Egypt, 238 ;
marks, 68
Flood of Thapangaing river, 206 ; period
of emptying basins, 19, 22 ; period of
filling basins, 19, 20, 22
Flood rivers, characteristics of, 12 ; the
Euphrates, 3 ; the Nile, 3 ; the Pun-
jab, India, 25
Flood rotations, 183, 184, 185
Flood season, crops, 25 ; Egypt, 3, 38 ;
Mesopotamia, 3
Flood spill channels, 238 ; surface slope,
68 ; system of inundation, 28 ; water
for fertilisation, 255
Floods, comparison, Egypt and Meso-
potamia, 3 ; Egypt, 12 ; Mesopotamia.
12 ; of the Euphrates, 3, 12 ; of the
Indus, 12 ; of the Nile, 12 ; of the
Tigris, 3, 12 ; Sind, India, 12 ; un-
ilooded areas in, 18
Floor, Assiout barrage, 142 ; Zifta bar-
rage, 142
Floors, ashlar covering of, 116, 141, 142 ;
below falls, 195, 196 ; of head sluices,
192 ; of homogeneous material, 142 ;
of regulating works, 192
Flow irrigation. See Free-flow
Flow-off and reservoir capacity, 70 ;
catchment, 59, 67, 68 ; of rainfall, 64,
€$, 66 ; statistics, 65, 66
Flow period of basin feeders, 20, 21 ; or
base of "duty," 40
Flumes, 207
Flush irrigation. See Free-flow
Forces acting on weirs, 116
Formulas of catchment discharge, 69 ;
irrigation, 269 — 277
Foundation borings, 74 ; springs, 143 —
150, 166 ; wells, 123 ; wells of Nadrai
aqueduct, 154
Foundations by cement grout, 157 — 163,
166, 167 ; by compressed air, 153; by
well-sinking, 153, 154 ; got in by
pumping, 143, 145, 149, 150 ; methods
of getting in, 142 — 170; of dams, 59,
71, 73, 75 ; of Delta barrage grouted,
163, 164, 165 ; of syphons, 209, 211
Fouracres' shutters, 125
Foy Sagar Tank dam, 77, 80
France, canal management, 232 ; curved
dam, 92 ; Furens dam, 82 ; Gros Bois
dam, 102 ; Government supervision,
235 ; inland waterways, 259 ; intervals
between w.\terings, 39 ; irrig?tion in,
10 ; land values, 10 ; navigable water-
ways, 235
Fiance, North of, rainfall, I ; rotations,
215 ; South of, "duty" of water, 39;
Verdon dam, 102 ; water rates, 227
French type oi river regulator, 107, 112
Freeflow drainage, 255 ; irrigation, 25,
182, 183, 25s
Free-fall weirs, 199
Fuel for pumping, 256, 257
Full supply level, 184
Furens dam, 82, 87, 88, gi
" Furrows," South Africa, 27
Gate recess of locks, 262, 264
Gates of barrs^es, Egypt, 1 27 J of Delta
barrage, 137 ; of Kosheshah escape,
I94i '95 ; °f locks, 262, 263 ; of
undersluices, 125, 126 ; of wood, 202 ;
of wrought iron, 201, 202 ; Reinold's,
loi, 102 ; Stoney's, 126, 127, 134,
202 ; with rollers, 201, 202
Ganges canal distributaries, 180, 181 ;
drainage, 186 ; loss of water in, 35 ;
Lower, and Nadrai aqueduct, 67 ;
Rutmoo crossing, 207 ; weirs, 86
Ganges, training of river, 246
Garda, Lake, 46
Gauge, uniformity of, 259
Geneva, Lake, 46
Genii river, source of Granada supply,
109 ; water-wheels, 106
Germany, inland waterways, 259
GhSts, India, 58, 60
Giza pumping station, Egypt, 138
Godaveri canal system, 258 ; weir, 114
Gordon, Mr. W. B., on Cape Colony,
26, 27
Government control of irrigation, 228,
232 ; Departments of Irrigation, 329,
230 ; duty regarding storage works,
$8 ; duty regarding water supply, 235;
INDEX
295
engineers, duties of, 228, 229 ; respon-
sibility, 236 ; supervision of waterways,
235
Gradient hydraulic, 117, 120, 121; of
canals, 173, 177 ; of drains, 189 ; of
flood in flow-off streams, 68
Gradients of flood canals, 25
Grading of canals, no, III
Granada, irrigation, 109 ; Moors first
engineers of, 10 ;■ water rates, 228
Grand anicut of Madras, 29, in
Great lakes of St. Lawrence basin, 33
Gros Bois dam, 102
Gross area of crop, Egypt, 37, 178
Grouted area of lock foundation, 162
Grouted blocks, dimensions of, 161
Grouting apparatus for blocks, 158, 159;
apparatus for piles, 152, 156 ; founda-
tions of Delta barrage, 163, 164, 165 ;
to get in ends of pipe syphon, 168,
169 ; joints, Detroit tunnel, 170 ;
pitching, 121 ; lock foundations, 161
— 163 ; well interval pipes, 156, 157
Groynes for river training, 246
Guadalquivir river, 39, 172
Guiding spurs above weirs, 116, 119;
below escapes, 197
Gwynne centnlugal pumps, 139, 257
H.
Hammurabi and irrigation in Chaldea,
4, 7, 28, 29
Harbours, basins as lock chambers in,
261
Hasisatrs, Chaldean Noah, 5
Heading up by river regulator, no, in
Head of canal, " duty " at, 41
Head on Delta barrage, 130, 131 ; on
Kosheshah escape, 194 ; on Zifta
barrage, 133
Head reach of canal, no, in
Head sluice floor, 192 ; of basin feeder,
21, 22, 23 ; of branch canals, 192 ; of
main canal, 174, i93. '9i. 192 i v™ts,
191
Head works of Granada canals, 109
Henares canal, water rates, 228 ; weir,
Spain, 85, 86
Hermitage breakwater, Jersey, grouting,
164
Herodotus and Lake Moeris, 29, 47 ; and
Mesopotamia, 4
High Line canal bench flume, 207
Higham, Sir T. , on Indian Irrigation,
58 ; on Marikanave reservoir, 90, 91
Himalayas, rainfall, 2
Holland, windmills, 105 ; land reclama-
tion, 253
Horiiontal closure of vents, 200, 201
Horse power, Divi pumps, 139 ; of
pumps, Komombos, 139 ; of pumps.
Lower Egypt, 139 ; pumping, 138, 139
Humid conditions, U.S. A., 2 ; region,
rainfall, 46 ; region traversed by St.
Lawrence river, 46
Humidity affecting evaporation, 35
Hydraulic formulas, 269 — 277 ; gradient,
117, 120, 121 ; power, Assuan lock,
263
I.
IBRAIUUIA canal syphon, 168
Idaho canal, Camere curtain, 202
Impermeable apron, 130
Impermeable floor, 132
Impermeable platform, 121, 130
Inclines on navigation canals, 262
India, aqueducts, 204, 205 ; areas irri-
gated, 8, 62 ; area under wells, 43 :
Betwa dam, 84 ; Bhatgarh dam, 95.
96, 100, 102 ; capacity of reservoir,
33 ; capital expenditure, 8 ; Coleroon
anicut, 135 ; crops, 37 ; dam and
storage, 59 ; development, 63 ; Divi
pumping scheme, 257 ; " duty " ol
vrater, 32, 33, 36—39, 41 ; earthen
dams, 72 ; flood canals, 26 ; flood
crops, 25 ; flow-off; 65, 66 ; form of
spurs, 243 ; formation of deltas, 13 :
foundations by well-sinking, 153 ;
Ganges and Bari Doab canals, 35 ;
Ganges canal weirs, 86 ; Government
controls irrigation, 228 : history of
irrigation of, 7 ; increase due to irri-
gation in, 8 ; irsndation canals, 18 ;
inundation in, 25, 26: Irrigation
Department, 229; main canal cross-
section, 179 ; Marikanave dam, 89,
90, 102, 103 ; Nadrai aqueduct, 67,
68; navigable cakals, 259 ; navigable
296
INDEX.
waterways, 258 ; needle closure, 200 ;
Nira dam or weir, 87, 88; Penner
river regulator, iz6, 134 ; Periyar
dam, 88, 89 ; profit on expenditure, 8 ;
pumping for irrigation, 139 ; rainfall,
I ; reservoir escapes, 69, 70 ; restric-
tion of cropped area, 222, 223 ; re-iults
of irrigation, 8 j rice crop, 38 ; rich in
population, ,^256 ; river banks, 237,
240; rivers of Upper, snow-fed, 45 ;
rotations, 216, 217 ; silting up of
reservoirs, 92, 95, 96 ; Sone anicut,
113; storage reservoirs, 58; syphons,
209, 210 ; tank irrigation, 61, 62 ;
tanks, 104; the l&t or picottah of,
104 ; the mote of, 104 ; three river
project, 61 ; training works, 246 ;
value of crops, 8 ; watering periods,
38 ; water rates, 226 ; waterways
public, 23s ; years of drought, 8
Indian Irrigation Commission, 58 ; type
of river regulator, 107, 112, 114; weir
of the future, 134 ; weirs, crest shutters
of, r2S
Indus river, 12, 25, 45
Infiltration, 180, 182, 183
I nflow of lakes, 32
Inflow of reservoirs, 48
Inland waterways, 259
Inlet regulator, 22
Inlets for drainage, 203
Inlets of lock sluices, 264
Insubmergible dams, 83
Intervals between foundation wells, 154,
15s. 156
Intervals between waterings, 34, 36 — 39
Inundation areas, 26 ; by flood, 13, 14 ;
canals, 14, 15, 138 ; canals, gradients
of, 25 ; canals, India, 25, 26 ; canals,
silt in, i8,> 19 ; control of, by Egyp-
tians, 3 ; in India, 25, 26 ; India and
Egypt compared, 25, 26; irrigation,
Egypt, 3 ; irrigation, Mesopotamia, 3 ;
natural, 3 ; of basins, depth of, 20, 22 ;
protection from, 28.
Inundation. See also Flood
Iron aqueducts, 207
Iron sluice gates, 201
Irrigable area, 2I2
Italian " duty " of water, 38
Italy, distribution of water, 222 ; Irrigation
Association, West of the Sesia, 222,
230; irrigation in, 10; land reclama-
tion, 253 ; modules, 214 ; Po embank-
ments, 240 ; rotation periods, 214,
215 ; watercourses public, 235 ; water
rates, 227
Java, irrigation administration, 230 ;
land tax, 226 ; rotation system, 216,
223 — 225 ; water rates, 226
Jhelum river, 6i
K.
Kair tank dam, 77, 78
Kali Nadi aqueduct See Nadrai aque-
duct ; discharge, 67
Kassassin pumping station, 257
Kennedy's velocity formula, 175, 176
Kharrds undersluice, Algeria, 93
Kharif crops, 25, 26, 37 ; " duty," India,
39 ; season, 37
Khartoum, Nile above, 52, 53
Khatatbeh pumping station, 135, 136
ICistna river, pumping from, 257 ; weir,
III, 114
Komombos plain, 138, 139
Kosheshah escape, 194, 19 J
Kurun Lake, Egypt, 2f
Lado on Upper Nile, 53
La Grange dam, 83, 84
Lake Albert, 46, 54, 55, 56, 57 ; Albert
Edward, 46 ; Baikal, 46 ; Como, 46 ;
Constance, 46 ; discharges, 32 ; Garda,
46 ; Geneva, 46 ; inflow and outflow,
32 ; Kurun, 29 ; levels, 32, 45 ;
Maggiore, 46 ; Mareotis, 256 ; Moeris,
29' 30. 47. 52 ; Neuchatel, 46 ; Nyassa,
46 ; source of supply, 32 ; sources of
rivers, 45, 46 ; Tanganyika, 46 ;
Tsana, 2 ; Victoria, 46 ; Whiting, 97
Lakes, Africa, at White Nile sources, 46,
52, 54 ; at river sources, 45, 46 ;
natural reservoirs, 48 ; of St. Lawrence
basin, 33, 45, 46 ; on Mississippi, 47 ;
Russia, 47
INDEX.
297
Land, configuration of, 31 ; bordering
Mediterranean, level of, 29 ; reclama-
tion, 253 — 256 ; surface, raising of,
237, 238 ; surface slope, 260 ; suvface
slope of basins, 19, 20; tax, Egypt,
226 ; tax, Java, 226
Laud values, basin and perennial irriga-
tion, 28 ; Castellon, Spain, 1 1 ; Egypt,
7; France, lo ; Madrid, 11; Murcia,
Spain, II ; Spain, 11; Transvaal, 9,
10 ; United States, 9
Laiamie river, 60
Lit of India, 104
Leaf gate of locks, 262, 263
Level crossing escape, 22
Level crossings for drainage, 203, 204,
206, 207
Level, mean flood, 20, 21
Levees, America, 240
Levels, fluctuation of lake, 45
Levels of lake observations, 32
Levels of river affected by rainfall, 45
Lift drainage, 255
Lift, Divi pumps, 140, 257
Lift irrigation, 182, 183, 255
Lift, Komombos, 139
Lift of locks, 265
Lift of pumps, Upper Egypt, 138
Lifting apparatus, 43
Lifting water, cost of, 139, 140
Lifls on navigation canals, 262
Limitation of water supply, 252
Line for irrigation canal, 258 ; navigation
canal, 258
Lock chambers, 261 ; chamber walls,
264, 265 ; dimensions, 262 ; founda-
tions grouted, 161 — 163; sites, 260;
sluice inlets, 264 ; sluice outlets, 263,
264 ; Zifta barrage, 264, 265 ; gates
^d sluices, 261 — 264
Locks and silt deposit, 264 ; Assuan
dam, 262, 263, 266 ; cracks during
construction, 266 ; double, 265 ; fill ng
and emptying, 263 : ladder of, 265 ;
lift of, 265 ; on navigable canals, 195 ;
settlement, 266 ; unifortn gauge, 259
Lombardy and irrigation, 10
Loose rock dams, 71, 79, 80
Lorca, Moors first engineers of, 10
Lorca water rates, 228
Loss by evaporation and absorption, 31,
35. 48, 50. 52-57.70, 71. 216
Loss of water in transit, 36, 63
lower Egypt irrigation, 129, 135 ; Nile
banks, 239, 240 ; pumps, 139 ; silt
deposit, 177 ; weUs, 44
Low-lying lands, 253, 255
Low supply, Nile, 37
M.
Madras, Cauvery weir, i9 ; consolidated
rate, 227 ; Divi pumping project, 257 ;
Godaveri canals, 258 ; Grand anicut,
29, III; Province, rainfall, 2 ;
pumping, 139 ; Ryves' formula used,
69 ; tank system, 61, 62 ; land values,
II
Madura irrigated from Periyar catchrtient,
60
Maggiore, Lake, 46
Mahanadi weir, 114, 116
Mahmudia canal, 137
Main canal discharges, 185 ; irrigation,
179
Main canals, alignment of, 171 ; water
surface, 179, 180
Main drains, r87j 188, 189
Maladevi tank dam, 73, 75
Malaga water rates, 228
Mareotis Lake, 256
Marikanave dam, 89, 90, 102, 103
Marikanave reservoir, 89, 90, 91
Marshes, Nile, channel through, 55, 56,
57
Marshes on Nile, 47, 52 — 57
Masonry cores, 75, 76 ; dams, 71, 72, 78.
80 ; works classified, 190
Mataana pumping station, 1 38
Material of lock gates, 262 ; of spurs and
revetments, 243, 248
Materials of construction, 141
Mattresses for river training, 249
Mead, Mr. Elwood, on control of irriga-
tion, 233, 234 ; on history of irrigatidn,
U.S.A., 29; on irrigation in U.S.A.,
8,9
Measure of ' ' duty " of water, 32 ; units
of, 33. 34
Mediterranean and Nile branches, 137 ;
lowlands bordering, 29
298
INDEX.
Mehemet Ali, 29, 128
Mesopotamia, 3, 4, 6, 7, 12, 45
Meters for water measurement, 213
Mex pumping station, 256
Mexico, arid regions of, 9
Midnapore canal system, 258
Miner's inch, 34
Mississippi, 47, 248, 249
Missouri river protection, 249
Modesto district, California, 9
Modules, 213, 214
Moeris, Lake, 29, 30, 47, 52
Montana, " duty " of water, 39
Moors and irrigation, 10, 109
Mote of India, 104, 105
Mougel and the Delta barrage, 128
Msta river, Russia, 47
Multan district, 25
Mundaring dam, 88, 102, 103
Murcia, Spain, land values, 11 ; Moors
first engineers of, 10
N.
Nadrai aqueduct, 67, 68, 154, 204 — 206
Naga Hamadi pumping station, 1 38
Nahrwan Canal, 6
Narora weir, 114 — 122
Nasbahs of Fayum, 199, 200
Navigable canals, 175, 195, 259 ; con-
ditions, 248 ; waterways, 258
Navigation canal, 258 ; inland, 47—49,
258 — 266 ; on irrigation canals, 258 ;
St. Lawrence river, 46 ; suitable
velocity for, 259, 260
Needle closure, 200
Neuchatel, Lake, 46
New Croton dam, 76, 90, 91, 100—103
Newell, Mr. F. H., on " duty " of water,
39 ; on the arid regions, U.S.A., 9
New Mexico, ancient irrigation works, 30
New York, New Croton dam, 76 ;
Quaker Bridge dam, 102 ; water
supply, 91
Neville's rule for distributary section,
181, 182
Nile above Kharioum, 52, 53
Nile, a flood river, 3, 12 ; and Lake
Moeris, 29 ; Assuan dam, 38, 96 —
100; hanks, 238 — 240; channel
through " Sudd," 55, 56, 57 ; delta,
rate of rise of, 238 ; discharge, 50 ;
effect of solid dam on, 98 ; Egypt's
carrier of raia water, 43 ; lakes, 46 ;
low supply, 37 ; marshes, swamps, or
Sudd, 47, 52 — 57 ; regulators, 128 ;
results of eflScient control of, 6 ; stor-
age in equatorial lakes, 52, 54, 56, 57 ;
storage uf surplus, 49 ; subsidiary weirs,
124 ; temporary dams, 137 ; valley,
deltaic, 13 : valley, inundation in, 13;
valley reservoir, 52
Nira canal superpassage, 209 ; dam, 86,
88
Normandy, prosperity due to irrigation,
10
Northern India, canals still possible, 58
Notch falls, 196, 198, 199
Notch form for falls, 198
Nyassa, Lake, 46
O.
Off-take channel of basin feeder, 22 ;
of main basin feeders, 18, 19
Ogee fall, form of, 85, 86, 195
Ohio river, 108
Okhlaweir, 114, 123
Opis, present aspect, 5
Orchard cultivation, 39
Orissa canal system, 258
Outflow of Albert Nyanza, 56 ; lake
sources, 32 ; Lake Albert, 55 ; reser-
voirs, 48
Outlet of Albert Nyanza, 57 ; dams, 76 ;
earthen dams, 72
Outlets of lock sluices, 263, 264
Outlets, rotation by, 217
Over-watering, 251, 252
P.
Parallel distributaries, 180
Pearson's theory of dam stresses, lOO
Penner river rqjulator, 126, 134
Percolation downwards into drains, 253,
255 ; supply obtained from, 137 ;
under dams, 74 ; under barrages,
132; under weirs, 1 17, 121
Perennial irrigation, Mesopotamia, 4;
Upper Egypt, 138
Perennial irrigation system, 28, 29, 30
Perennially irrigated land, value of, 28
INDEX.
«99
Period for calculating "duty," Egypt,
42 ; of flow, 40 ; of pressure or
greatest demand, 41, 42 ; of supply,
214, 319
Periods between waterings, 34, 36 — 39
Periyar dam, 60, 88, 89
Periyar river, 60, 61
Permeable spurs, 248
Persian wheel, 104, 105
Pharaohs, records of, about irrigation, 7
Philae, submersion of, 51, 70
Picottah of India, 104
Piedmont, plains of, 10 : irrigation con-
trol, 230, 231 ; water charges, 227
Piles, as curtains, 132 : cast iron, 151,
'S*. 'SS ! grouting joints of, 152;
rows of, 130, 132, 133. 147
Piling. See Piles
Pipe syphons, construction of ends, i68,
169 ; method of laying, 167, 168 ;
without concrete, 211
Pipes, sub-irrigation from, 39
Piping, or leakage under floor, 115, 116,
119, 122, 129
Po river, 46
Fo valley land reclamation, 253
Poirfe dams, 107
Pooling below regulators, 197
Population, Dongola, 105 ; wanted for
reclamation, 255
President Roosevelt's Message to Con
gress, 58
Pressure, or greatest demand, period, 41.
42
Pressures, Assuan dam, 99 ; in dams,
102, 103; in syphons, 208, 209; on
weirs, 116 — Jl8, 120, 121
Priorities, United States, 224, 225
Products raised by canal, 259 ; trans-
ported by canal, 259
Profit on expenditure, India. 8
Programme of emptying basins, 23, 24 ;
of filling basins, 23, 24
Programmes of rotations, 217 — 221,
223 — 225
Project, based on " duty," 34 ; canal,
30 ; for a basin system, 19 ; for Nile
storage, 49 ; irrigation, 40 ; storage,
59; three-river, India, 61
Protective apron, Assuan dam, 100 ;
banks, 14, 237—243; banks, action
of, 13 ; material for banks, 241 ; revet-
ments or pitching of banks, 24, 242,
243 ; spurs, 242, 243 ; wall of basin
banks, 24
Puddle clay apron, 119, 120, 122; core,
75. 76. 78 i face to dam, 78 ; trench,
74. 75
Pumping, expenditure, 256, 257 ; fur
reclamation, 253, 254, 255 ; India,
139. 257
Pumping station, Divi, India, 139;
horse-power, 138, 139
Pumping stations, 105, 106, 129, 135,
256, 257 ; Giia, 138 ; Upper Egypt,
138
Pumps, Atfeh, 137 ; in Upper Egypt,
138 ; Komombos, 139; on main drains
257; period of working, 2i8, 219, 220
used in irrigation, 106 ; used in
reclamation, 244, 255, 257; worked
by electricity, 257
Punjab, crops, 37; inundation canals,
25 ; rainfall, I
Q.
QtJAKER Bridge dam, maximum pres-
sure, 102 ; replaced by New Croton
dam, 91
Quantity of water, rate levied on, 213
Quantity of wqter required for irrigation,
36, 37. 38. 40, 41
R.
Rabi crops, India, 25,26, 37; "duty"
for, 41 ; season, 37 ; sowings, 41
Rain, its effect on "duty' value, 42
Rain reaching Lake Albert, 56
Rain water, rivers carriers of, 43 ; versui
well water, 44
Rainfall, Abyssinia, 2 ; and reservoir,
63, 64, 65 ; capriciousness of, 31 ;
catchment area, 2 ; Central Provinces,
India, 2 ; deficiency, 31 ; deficiency,
India, 8 ; distribution of, I, 2 ; effect
on river levels, 45 ; Egypt, 2. 3 ;
England, I ; flow-off, 64, 65, 66 ;
Gh^ts, India, 60 ; Himalayas, 2 ;
humid regions, 46 ; India, i ; lost by
evaporation, 47 ; Madras Province, 2 ;
300
INDEX.
Mesopotamia, 3 , North of France, I ;
not constant, 41 ; of arid legiuns,
U.S.A., 9; of catchments, 43; of
region to be irrigated, 31 ; Periyar
catchment, 60 ; primary source of sup-
ply, 43 ; Punjab, India, I ; record, 64,
68 ; run-off, 2 ; Sind, i ; source of
irrigation, 2 ; statistics, 64, 68 ; Sudan,
2 ; U.S. America, 2 ; West Coast of
India, 2 ; Western Ghats, India, 58
Rain-fed rivers, 45
Rainy region, Abyssinia, 2 ; Sudan, 2
Raising of land surface, 237, 238 ; of
river bed, 237, 238
Rankine's rule for puddle cores, 75
Rapids, 194, 196
Rates for water, used in irrigation, 213,
226 — 228 ; America, 227 ; Egypt, 226 ;
France, 227 ; India, 226 ; Italy, 227 ;
Java, 226 ; Spain, 227, 228
Ravi river, 61
Ravi syphon, 209, 210
Reach of canal as lock, 261
Rechna Doab and Chenab canal, 7
Reclamation by deep drains, 253, 255 ;
by pumping, 253, 254 ; by surface
washings, 253, 254 ; by training rivers,
248 ; of land, 253 — 256 ; use of flood
virater in, 255 ; want of population for,
2SS. 256
Reference books, 278 — 281
Regulating apparatus, 200 — 202
Regulating falls, 177
Regulating works of basins, 21
Regulator, Egyptian type, 131, 132 ; for
river reclamation, 248 ; inlet, 22 ; on
navigable canal, 260, 261 ; Penner
river, 126, 134 ; river, 109, no, in
Regulators, basin, design of, 23 ; Nile,
12S ; of basins, 15, 16, 17, 21 ; of
Lake Moeris, 48 ; of rivers, 107 ; on
canals, 193 ; river, of the future, 134
Reinold's gates, loi, 102
Remission of land tax, 226
Replenishment of reservoir, 64, 67
Reservoir, absorption in, 41 ; Assuan, 41,
51. 52. 56, 97—99, 22 r ; Bhatgarh,
97 ; bywash, 67 ; capacity of, 33 ;
dam, 57, 58, 59; '-duty" at, 41;
Egypt, 49> so; f scape, 65, 67, 69;
evaporation in, 41, 50'; features of
59 ; filling of, 63 ; in Nile valley, 52 ;
Lake Moeris, 29, 48 ; Lake Tsana, 2 ;
Marikanave, 89, 90, 91 ; Periyar, 60 ;
project, 67, 68; replenishment, 64,67 ;
site, 59, 63, 64, 70 ; site for Egypt, 50 ;
source of supply, 48 ; storage capacity,
50, 70 ; study, 68 ; study by Willcocks
in Egypt, 50 ; supply from, 48 ; waslc
weirs, 69 ; water " duty, ' ' 40
Reservoirs, artificial, 47, 48, 57, 58 ;
conditions favouring, 63 ; demand for,
63 i for storage, India, 58 ; Govern-
ment work, 236 ; inflow and outflow,
48 ; natural, lakes as, 45—48 ; natural,
snowfields as, 45 ; river-fed, 62 ; Rus-
sia, 47 ; South Africa, 59 ; silt deposit
in, 92, 95, 96, 98 ; source of supply,
104 ; United States, 58
Results of Assuan dam, 28 ; of efficient
control of Nile, 6 ; of irrigation, 4, 1 1 ;
of irrigation in France, 10 ; of irriga-
tion in India, 8 ; of irrigation in Spain,
II ; of neglect of irrigation, 1 1
Retirement of river banks, 242, 243, 248
Reverse lock gates, 263
Revetments for bank protection, 242,
243
Revetted slopes ol regulating works,
192
Reynolds, Mr. B. P., on weirs, 134
Rhine, moderated by lakes,- 46 ; river
banks, 240
Rhone, moderated by lakes, 46
Rice crop, Egypt, 37 ; India, 38
Rice, "duty," 38
Rice irrigation, 220, 221, 223 — 225
Rice, Italy, 38
Rice, water allowance, 222, 223
Rio Grande, ancient irrigation on, 30
River Cauvery weir, 29 ; Chenab, 61 ;
Congo, 46 ; Darro, 109 ; Detroit
tunnel, 169, 170 ; Genii, 109 ; Genii
and waterwheels, 106; Guadalquivir,
39, 172 ; Jhelum, 61 ; Laramie, 60 ;
Mississippi, 47 ; Msta, 47 ; Ohio, 108 ;
Penner regulator, 126, 134 ; Periyar,
60, 61 ; Po, 46 ; Ravi, 61 ; Rhine, 46 ;
Rhone, 46 ; Shire, 46 : Sobat, 55 ; St.
Lawrence, 46 ; Thapangaing^ 206 ;
INDEX.
301
Va^ai,6o, 61 ; Volga, 47 ; Yenisei, 46 ;
Zak, South Africa, 26 ; Zambezi, 46
River banks, 24, 25, 237—243 ; bed,
raising of, 237, 238 ; bed reclamation,
248 ; capacity, 238 ; dams, 106, 107 ;
delta, growth by deposit, 12 ; discharges
31 ; encroachments, 243 ; gauges,
31 ; levels, eSect of rainfall on, 45 ;
natural discharge, 49 ; regulators, 107,
109, no. Ill ; regulators of the future,
134 ; spurs, 247, 248 ; training works,
245-249; velocity, 173, 174, 175;
weir alignment, 114 ; weir. South
Africa, 26
River-fed reservoirs, 62
Rivers, carriers of rain water, 43 ; fed
by rain, 45 ; fed by snow, 45 ; in
flood, 12 ; Nature's waterways, 43 ; of
flood, characteristics of, 12 ; of flood,
the Euphrates, 12 ; of flood, the Indus,
12 ; of flood, the Nile, 12 ; of flood,
the Tigris, 12; ofiiake of basin feeders
from, 18, 19; principal source of
supply, 45 ; source of supply, 31 ;
with lake sources, 45, 46
Rockfilldams, 71, 79, 80; weir, 109
Rocky Mountains, Colorado, flow-ofl'
diversion through watershed, 59
Roosevelt, President, Message to Con-
gress, s8
Rosetta branch of Nile, 135, 137 ;
barrage, 128 ; weir, 131
Ross, Col. J. C, on canal off-takes, 19
Rotations, ^ypt, 216, 218 — 222 ; France,
2IS ; Italy, 214, 215 ; Java, 216, 223
— 225 ; Spain, 215 ; advantages of,
216, 217 ; by distributaries, 217 ; by
outlets, ai7 ; during flood, 183, 184,
185 ; programmes of, 217 — 221, 223 —
23S ; system, 180, 183, 184, 214—225
Run-off' of rainfall, 2
Run-off. See also Flow-oft
Russia, reservoirs serving navigaljle
rivers, 47
Rutmoo torrent level crossing, 207
Ryves' formula, 69
" Saai " dams, South Africa, 27
South Africa, development and storage,
236
Sakia, 104, 105
Salt efflorescence, 182
Salt lands, 253
Salt washings, 183
Salvador, M., on cost of preparing land,
250
San Diego flume, 207
San Joaquin drainage, 186
Scott- Moncrieff, Sir C, and Egypt, 136 ;
on control of irrigation, Italy, 230,
231 ; on distribution, 222 ; on land
values, France, 10 ; on Southern
Europe, 39 ; on well irrigation, 44
Scour of canal bed, 175
Scouring below weirs, IIJ ; by lock
sluices, 264 ; sluices, 107, 113 ; sluices
of dams, 92 — 96 ; undersluices, 174
Season, irrigation, 215, 224
Season, irrigation of, rate assessed on,
213
Seasons of greatest discharge, 177, 178
" Second-foot," 33
Settlement of locks, 266
Shadouf, 104, 105
Sheet-piling, 150
Shubra well intervals, 156, 157
Shutters, Boule, 107, 108; crest, 112,
"3> 123, 125; of undersluices, 125;
Smart's, 126; Stoney's, 126, 127, 134,
202 ; working of, to exclude silt, 174
Sill on floor of falls, 195.
Silt. See also Deposit
Silt deposit, 24, 25, 173—177, 217 ; above
anicuts, 112, 113, 114; locks, 264;
staunching action of, 35
Silt disposition, 237, 248
Silt, deposits in canals, 193 ; exclusion
through design of head sluice, igo,
igi ; in floods, 183 ; inundation canals,
18, 19 ; observations on Sirhind canal,
176 ; reservoirs, 92, 95, 96, 98
Silting of basin feeder, 21
Sind canals, 58 ; needle closure, 200
Sind , inundation canals, 25, 26 ; irrigated
by flood, 12 ; rainfall, I ; water rates,
227
Sirhind canal, silt observations, 176
Site of reservoir and dam, 59, 63, 64, 70
302
INDEX.
Site ol river regulator, 109, HO, 113
Sites of falls, 260
Sites of locks, 260
Sky line ditch, 60
Slope of land surface, 19, 20, 173, 177 ;
water surface. 19, 20, 21, 173, 177
Sluice capacity of locks, 262, 263 ; inlets
in locks, 264 ; outlets in locks, 263,
264
Sluices, lock gates, 263, 264 ; lock walls,
263, 264 ; of basins, 21 : of locks, 261 ;
scouring, of dams, 92 — 96
" Sluit " channels. South Africa, 26
Smart's shutters, 126
Snow-fed rivers, 45, 61
Snowfields, Nature's reservoirs, 45
Solani aqueduct, 204
Sone aqueduct, 113; canal distribu-
taries, 181; weir, 114, 123, 125;
well-sinking for foundations of weir,
154
Source of supply, primary, rain&ll, 43 ;
principal rivers, 45 ; reservoir, 48 ;
springs and percolation, 137
Sources of rivers, lakes, 45, 46
Sources of supply, various, 31, 32, 51,
57. 104
Sowing of basin crop, 24
Sowings, rabi, India, 41
South Africa, development depends on
storage, 59, 63 ; irrigation of fiat lands,
26, 27
Southern Europe, " duty " of water,
33
Spain, Alicante dam, 92, 102;
Almanza dam, 102 ; Andalucia, 172 ;
dams, II, 82 ; form of spurs, 243 ;
Henaies weir, 86, 87 ; irrigation, 10,
109; irrigation administration, 231 ;
irrigation concessions, 231, 232 ; irri-
gating seasons, 40; results of irriga-
tion, 1 1 ; rotations, 215, 216 ; silting up
of reservoirs, 92 ; Val de Infiemo dam,
92, 98 ; water rates, 227, 228 ; water-
courses, public, 235 ; waterwheels, 106
Spanish " duty " of water, 39 ; nnder-
sluices, 93, 94, 95
Spill channels, flood, 238
Spring levels, raising of, 223
Springs, as source of supply, 43 ; closed
by cement grout, 1 50 ; in foundations,
143 — 150, 166; of river bed, 137
Spurs, for canal protection, 242, 243;
for river training, 247, 248 : guiding,
116, 119 ; to stop pooling. 197
Stability, Assnan dam, 99; of curved
dams, 91 ; of dams. 81
State control of irrigation, Wyoming, 234
Steel plate core, 79
Steel tube syphons, 211
St. Lawrence basin, 33 ; lakes, 45, 46 ;
river, 46
Stoney's shutters, 126, 127, 134, 202
Storage, 46, 47, 48
Storage by snowfields, 45
Storage capacity of Albert Nyanza, 56 ;
of reservoir, 33, 70 , of St. Lawrence
lakes, 46
Storage, Lake Albert, 57 ; Nile lakes,
52, 54, 57 ; of Assuan reservoir, 51
of Lake Moeris, 47 ; of Nile surplus,
49 ; Periyar, 60 ; required, 40, 41 ;
requirements of E^pt, 55, 56
Storage reservoir. See Reservoir
Storage reservoirs, conditions favouring,
63 ; demand for, 63 ; India, 58
Storage, South Africa, 59, 236 ; to sup-
plement natural discharges, 49 ; United
States, 58
Strange. Mr. W. L., on earthen dams
72 ; on fiow-oSE 65, 66
Stresses in dams, 81
Sub-irrigation bom pipes, 39
Subme^ble dams, 83
Subsidiary drains, 187, 188, 189
Subsidiary weirs, 83, 84, 131, 133
Subsidiary weirs of Egypt, 124, 157, 158
»S9
Subsoil drainage, 253, 254, 255
Sudan, as affected by lakes, 46 ; Doi^ola
irrigation, 104 ; Lake Tsana as reser-
voir for, 2 ; rainfall, 2
Sudd region, Nile, 47, 52 — 57
Sugar factories, 138
Summer rotations, 184, 185
Summer season irrigation, Egypt, 38 ;
Spain, 40
Summers, low, Nile, 37
Super-passages for drainage, 303—305.
309
INDEX.
303
Superstructure of head sluices, 192
Supply, accommodation to demand, 64
Supply and demand, 67, 212 — 214 ; by
pumpiijg, 135, 136 ; from percolationi
137 ; from reservoir, 48 ; New York)
91 ; navigation canals, 262 ; of water
from various sources, 43, 51, 57, 164 ;
of water to basins, 16, 17; period
during rotations, 214, 219 ; primary
source of, rainfall, 43 ; river source of,
31 ; livers, principal source of, 45 ;
source of reservoir, 48 ; underground,
43
Surface irrigation, 39
Surface washings, 253, 254
Sutlej river, 25
Sweetwater dam, 92
Syndicate of Valencia, 231
Syndicates of irrigators, 232
Syphon aqueduct, 208 ; canal, basin
system, 16, 18 ; Ibrahimia canal, 168 ;
laying under running canal, 167, 168 ;
masonry, design of, 208 — 211; pressure
due to head, 208, 209 ; under basin-
feeder, 21, 22 ; under Ravi river, 61
Syphons bent, 210, 211 ; blowing up,
208 ; for drainage, 203, 204, 208 — 21 1 ;
horizontal, 210, 21 1; of steel tubes,
211; of wood, 207; pipe, construction
of ends, 168, 169; pipe, method of
laying, 167, i68 ; waterway, 210
T.
Talus of Assuan dam, icxj ; of escapes,
197 ; of regulating works, 192 ; of
weirs, 115
Tanganyika Lake, 46
Tanks, India, 61, 62 ; source of supply,
104 ; United States, 62 ; waste weirs
of, 69, 70
Tatils, or rotations, India, 216
Temperature affecting evaporation, 31,
Thapangaing aqueduct and river, 206
Theory of dam construction, 81
Thomas and Watt on river training, 249
Tie-back of spurs, 244
Tigris, 3, 5, 6, 12, 45
Titicus dam, 91
Traffic, size of lock to suit, 262
Training rivers, 245 — 249
Transport for produce, 256 ; of goods by
canal, 259
Transvaal, land values, 9, 10
Trebeni canal head sluice, igo, 191
Trial pits, 74
Tribunal of waters, 23 1
Tunnel under Detroit river, 169, 170
Tunnels, 60
Turlock dam, 84, 85
Turlock district, California, 9
U.
Undskground supply, 43
Undermining of banks, 242, 243
Undersluice, See also Scouring sluice.
Undersluice shutters, 125
Undersluices, Assuan dam, 98— 100 ; of
weirs, 107, 113
United Provinces, India, crops, 37
U.S.A., aqueducts, 207 ; area of arid
regions, 9 ; dams and storage, 59 ;
irrigation in the, 8, 9 ; land values, 9 ;
levees, 240 ; Newell on arid regions,
9 ; priorities, 224, 225 ; rainfall, 2, 9 ;
storage reservoirs, 58 ; tanks, 62, 104 ;
water value, 9 ; West, drainage, 186 ;
West, miner's inch, 34
Units of measure of "duty," 32, 33, 34
Upper Egypt, and pumping, 138; basin
programme, 23, 24 ; barrage, I j2 ;
inundation in, 13 ; Komombos, J38,
139 ; wells, 44
Upper Nile above Khartoum, 52, 53
Upper Otay dam, 92
Urgel canal water rates, 228
Utah, " duty " of water, 39
Vaigai river, 60, 61
Val de Infierno dam, 92, 98
Valencia, irrigation syndicate, 231 j
irrigation works of, 10 ; Moors first
engineers of, 10 ; no water rates, 228
Value of cotton crop, 136
Value of crops compared, 28 ; India, 8
Value of land, basin and perennial, 28 ;
Egypt. 7
304
INDEX.
Value of time in navigation, 262, 263
Value of water, U.S.A., 9
Values of land, Castellon, II ; France,
10; Madrid, 11 ; Murcia, 11; Spain,
, II ; Transvaal, 9, 10; U.S.A., 9
Vaucluse, France, land values, 10
Vegas of Spain, 172
Velocity of canals, 216 ; of flow for
navigation, 259, 260 ; of flow in canals,
173—177; of flow in drains, 189; of
river flow, 173 — 175 ; through syphon,
210 ; to carry forward silt, 177
Vents of head sluices, 191 ; ofKosheshah
escape, 194, 195
Verdon dam, 102
Vertical closure of vents, 2(D0
Victoria Nyanza, 46
Village watercourses, loss in, 35
" Vleis " of South Africa, 26, 27
Volga and navigation, 47
Volume of water required for irrigation, 40
Vymwy dam, 84, 85, 86
W.
Wadi Kayan, 52
Wales, Vymwy dam, 84, 85
Walnut Grove dam, 79
Washing land, 253, 254, 255
Waste weirs, Bhatgarh dam, 96, 100,
loi ; of dams, 72, 76, 100, loi ; of
tanks and reservoirs, 69, 70
Water allowance, Egypt, 37, 38
Water ' ' duty." See ' ' Duty "
Water levels. Delta barrage, 132
Water, loss of, 31, 35, 36
Water meters, 213
Water rates, 213, 226—228
Water rates, America, 227 ; Egypt, 226 ;
France, 227 ; India, 226 ; Italy, 227 ;
Java, 226 ; Spain, 227, 228
Water supply, 31, 43
Water supply, decreed public, 235 ;
Egypt, 52, 56 ; limitation of, 252
Water surface of drains, 186
Water surface slope, canals, 173, 177,
260 ; flood canals, 19, 20, 21
Water value, U.S.A., 9
Watercourses, loss in, 35
Water-cushion below dams, 83, 84, 85 ;
below falls, 195, 196
Watershed, the scientific boundary, 2
Watersheds, 59, 60, 64
Waterspread, Feriyar leserroir, 60
Waterwheels, 106
Watering, depth of, 215
Watering, excessive, 251, 252
Watering periods, 34. 36 — 39
Waterings, intervals between, 212, 213,
215, 218, 219, 221, 222
Waterings, rate on number of, 213
Waterlogging, 180, 182, 186, 216, 223,
252
Watertight diaphragm of dams, 77, 79 ;,
junction of iron and masonry, 207, 208 ;
strata, 43
Waterway of drainage works, 206 ;
of-syphons, 210 ; safety margin, 192
Waterways for navigation, 258 ; Govern-
ment property, 235 ; inland, 259
Weeds in drains, 189
Weights and measures, 267, 268
Weir alignment, 114; Baiturnee, 114;
Brahmini, 114; Burra, 114; Cauvery
river, 29 ; Chenab, 114, 116, 121, 122 ;
core-wall for foundations, 154;
Egyptian, 114, 123—125, 134 ; Goda-
veri, 1 14 ; Henares, 85, 86 ; Indian,
134; Kistna, iii, 114; Mahanadi,
114, 116; Narora, 1 14— 122; Nira,
87, 88 ; of Delta barrage, 114, 122 —
125 ; Okhla, 114, 123
Weir, river, South Africa, 26 ; Rosetta
branch of Nile, 131 ; Sone, 114, 123,
Weirs, classified, 114-; Delta barrage,
use of cement grout, 157 — 159; forces
acting on, 116 ; free-fall, 199 ; Ganges
canal, 86 ; Indian, 125 ; parallel cur-
rents, 116; percolation below, 117;
piping, 115, 116, 119, 122, 129 ;
pressures on, 116 — 118, 120, 121 :
scour below, 115 ; subsidiary, 83, 84,
13I1 '33 ; subsidiary, Nile, 124
Well and canal water compared, 44, 45
Well irrigation, 43, 44
Well irrigation area, India, 62
Well sinking for foundations, 153, 154
Well water versus rain water, 44
Wells, area under irrigation, 43, 44
Wells in foundations, 123
INDEX.
305
Wells in foundations of Nadrai aqueduct,
IS4 : in head of Ismailia canal, 155 —
'57. I6S> '66 ; irrigation from, 2 ; of
curtain walls, 120 — 122; source of
supply. 43. 44. 104
West Coast of India, rainfall, a
Western, Col. J. H., and Delta barrage,
127
White Nile at Sobat river, 55 ; lakes, 46,
52.54
Whiting Lake, 97
Willcocks, Sir W., conclusions on silt
deposit, 176, 177 ; lecture on Chaldea,
5 ; on closing springs, 147, 148, 149 ;
on pumps in Egypt, 139 ; on pumping
stations, 257 ; on scouring sluices, 93 ;
on South Africa, 235, 236; reservoir
study, 50
Windmills, loj, 106
Wing walls of aqueducts, 205
Wings of falls, 196, 197
Wilson, Mr. H. M. , on " duty " of water,
U.S.A., 39 ; on safe pressures in
dams, 102
Wooden aqueducts, 207
Wooden gates, 202
Wooden syphons, 207
Wyoming code, 233
\.
Yakima valley, Washington, 9
Yenisei river, 46
Z.
Zak river. South Africa, 26
Zambesi river, 46
Zifta batrage, Egypt, 127, 131— 134
floor, 142 ; foundations, 145 ; lock,
264, 265; piles, 151, 155
Zirta, head sluice above barrage, 192
Zola dam, 92, 93
iniK WUll'KFRlARS fRSSS. LXS., LOMDON AMD lOHUSilOGM,